diff --git a/src/command/use/commands/brand.ts b/src/command/use/commands/brand.ts
index 6dac4b0dd07..fa521e6a219 100644
--- a/src/command/use/commands/brand.ts
+++ b/src/command/use/commands/brand.ts
@@ -16,7 +16,6 @@ import { TempContext } from "../../../core/temp-types.ts";
 import { downloadWithProgress } from "../../../core/download.ts";
 import { withSpinner } from "../../../core/console.ts";
 import { unzip } from "../../../core/zip.ts";
-import { templateFiles } from "../../../extension/template.ts";
 import { Command } from "cliffy/command/mod.ts";
 import { initYamlIntelligenceResourcesFromFilesystem } from "../../../core/schema/utils.ts";
 import { createTempContext } from "../../../core/temp.ts";
@@ -24,9 +23,194 @@ import { InternalError } from "../../../core/lib/error.ts";
 import { notebookContext } from "../../../render/notebook/notebook-context.ts";
 import { projectContext } from "../../../project/project-context.ts";
 import { afterConfirm } from "../../../tools/tools-console.ts";
+import { readYaml } from "../../../core/yaml.ts";
+import { Metadata } from "../../../config/types.ts";
 
 const kRootTemplateName = "template.qmd";
 
+// Brand extension detection result
+interface BrandExtensionInfo {
+  isBrandExtension: boolean;
+  extensionDir?: string; // Directory containing the brand extension
+  brandFileName?: string; // The original brand file name (e.g., "brand.yml")
+}
+
+// Check if a directory contains a brand extension
+function checkForBrandExtension(dir: string): BrandExtensionInfo {
+  const extensionFiles = ["_extension.yml", "_extension.yaml"];
+
+  for (const file of extensionFiles) {
+    const path = join(dir, file);
+    if (existsSync(path)) {
+      try {
+        const yaml = readYaml(path) as Metadata;
+        // Check for contributes.metadata.project.brand
+        const contributes = yaml?.contributes as Metadata | undefined;
+        const metadata = contributes?.metadata as Metadata | undefined;
+        const project = metadata?.project as Metadata | undefined;
+        const brandFile = project?.brand as string | undefined;
+
+        if (brandFile && typeof brandFile === "string") {
+          return {
+            isBrandExtension: true,
+            extensionDir: dir,
+            brandFileName: brandFile,
+          };
+        }
+      } catch {
+        // If we can't read/parse the extension file, continue searching
+      }
+    }
+  }
+
+  return { isBrandExtension: false };
+}
+
+// Search for a brand extension in the staged directory
+// Searches: root, _extensions/*, _extensions/*/*
+function findBrandExtension(stagedDir: string): BrandExtensionInfo {
+  // First check the root directory
+  const rootCheck = checkForBrandExtension(stagedDir);
+  if (rootCheck.isBrandExtension) {
+    return rootCheck;
+  }
+
+  // Check _extensions directory
+  const extensionsDir = join(stagedDir, "_extensions");
+  if (!existsSync(extensionsDir)) {
+    return { isBrandExtension: false };
+  }
+
+  try {
+    // Check direct children: _extensions/extension-name/
+    for (const entry of Deno.readDirSync(extensionsDir)) {
+      if (!entry.isDirectory) continue;
+
+      const extPath = join(extensionsDir, entry.name);
+      const check = checkForBrandExtension(extPath);
+      if (check.isBrandExtension) {
+        return check;
+      }
+
+      // Check nested: _extensions/org/extension-name/
+      for (const nested of Deno.readDirSync(extPath)) {
+        if (!nested.isDirectory) continue;
+        const nestedPath = join(extPath, nested.name);
+        const nestedCheck = checkForBrandExtension(nestedPath);
+        if (nestedCheck.isBrandExtension) {
+          return nestedCheck;
+        }
+      }
+    }
+  } catch {
+    // Directory read error, return not found
+  }
+
+  return { isBrandExtension: false };
+}
+
+// Extract a path string from various formats:
+// - string: "path/to/file"
+// - object with path: { path: "path/to/file", alt: "..." }
+function extractPath(value: unknown): string | undefined {
+  if (typeof value === "string") {
+    return value;
+  }
+  if (value && typeof value === "object" && "path" in value) {
+    const pathValue = (value as Record<string, unknown>).path;
+    if (typeof pathValue === "string") {
+      return pathValue;
+    }
+  }
+  return undefined;
+}
+
+// Check if a path is a local file (not a URL)
+function isLocalPath(path: string): boolean {
+  return !path.startsWith("http://") && !path.startsWith("https://");
+}
+
+// Extract all referenced file paths from a brand YAML file
+function extractBrandFilePaths(brandYamlPath: string): string[] {
+  const paths: string[] = [];
+
+  try {
+    const yaml = readYaml(brandYamlPath) as Metadata;
+    if (!yaml) return paths;
+
+    // Extract logo paths
+    const logo = yaml.logo as Metadata | undefined;
+    if (logo) {
+      // Handle logo.images (named resources)
+      // Format: logo.images.<name> can be string or { path, alt }
+      const images = logo.images as Metadata | undefined;
+      if (images && typeof images === "object") {
+        for (const value of Object.values(images)) {
+          const path = extractPath(value);
+          if (path && isLocalPath(path)) {
+            paths.push(path);
+          }
+        }
+      }
+
+      // Handle logo.small, logo.medium, logo.large
+      // Format: string or { light: string, dark: string }
+      for (const size of ["small", "medium", "large"]) {
+        const sizeValue = logo[size];
+        if (!sizeValue) continue;
+
+        if (typeof sizeValue === "string") {
+          if (isLocalPath(sizeValue)) {
+            paths.push(sizeValue);
+          }
+        } else if (typeof sizeValue === "object") {
+          // Handle { light: "...", dark: "..." }
+          const lightDark = sizeValue as Record<string, unknown>;
+          if (
+            typeof lightDark.light === "string" && isLocalPath(lightDark.light)
+          ) {
+            paths.push(lightDark.light);
+          }
+          if (
+            typeof lightDark.dark === "string" && isLocalPath(lightDark.dark)
+          ) {
+            paths.push(lightDark.dark);
+          }
+        }
+      }
+    }
+
+    // Extract typography font file paths
+    const typography = yaml.typography as Metadata | undefined;
+    if (typography) {
+      const fonts = typography.fonts as unknown[] | undefined;
+      if (Array.isArray(fonts)) {
+        for (const font of fonts) {
+          if (!font || typeof font !== "object") continue;
+          const fontObj = font as Record<string, unknown>;
+
+          // Only process fonts with source: "file"
+          if (fontObj.source !== "file") continue;
+
+          const files = fontObj.files as unknown[] | undefined;
+          if (Array.isArray(files)) {
+            for (const file of files) {
+              const path = extractPath(file);
+              if (path && isLocalPath(path)) {
+                paths.push(path);
+              }
+            }
+          }
+        }
+      }
+    }
+  } catch {
+    // If we can't read/parse the brand file, return empty list
+  }
+
+  return paths;
+}
+
 export const useBrandCommand = new Command()
   .name("brand")
   .arguments("<target:string>")
@@ -100,8 +284,44 @@ async function useBrand(
   // Extract and move the template into place
   const stagedDir = await stageBrand(source, tempContext);
 
-  // Filter the list to template files
-  const filesToCopy = templateFiles(stagedDir);
+  // Check if this is a brand extension
+  const brandExtInfo = findBrandExtension(stagedDir);
+
+  // Determine the actual source directory and file mapping
+  const sourceDir = brandExtInfo.isBrandExtension
+    ? brandExtInfo.extensionDir!
+    : stagedDir;
+
+  // Find the brand file
+  const brandFileName = brandExtInfo.isBrandExtension
+    ? brandExtInfo.brandFileName!
+    : existsSync(join(sourceDir, "_brand.yml"))
+    ? "_brand.yml"
+    : existsSync(join(sourceDir, "_brand.yaml"))
+    ? "_brand.yaml"
+    : undefined;
+
+  if (!brandFileName) {
+    info("No brand file (_brand.yml or _brand.yaml) found in source");
+    return;
+  }
+
+  const brandFilePath = join(sourceDir, brandFileName);
+  // Get the directory containing the brand file (for resolving relative paths)
+  const brandFileDir = dirname(brandFilePath);
+
+  // Extract referenced file paths from the brand YAML
+  const referencedPaths = extractBrandFilePaths(brandFilePath);
+
+  // Build list of files to copy: brand file + referenced files
+  // Referenced paths are relative to the brand file's directory
+  const filesToCopy: string[] = [brandFilePath];
+  for (const refPath of referencedPaths) {
+    const fullPath = join(brandFileDir, refPath);
+    if (existsSync(fullPath)) {
+      filesToCopy.push(fullPath);
+    }
+  }
 
   // Confirm changes to brand directory (skip for dry-run or force)
   if (!options.dryRun && !options.force) {
@@ -125,10 +345,18 @@ async function useBrand(
   }
 
   // Build set of source file paths for comparison
+  // Paths are relative to the brand file's directory
+  // For brand extensions, the brand file is renamed to _brand.yml
   const sourceFiles = new Set(
     filesToCopy
       .filter((f) => !Deno.statSync(f).isDirectory)
-      .map((f) => relative(stagedDir, f)),
+      .map((f) => {
+        // If this is the brand file, it will become _brand.yml
+        if (f === brandFilePath) {
+          return "_brand.yml";
+        }
+        return relative(brandFileDir, f);
+      }),
   );
 
   // Find extra files in target that aren't in source
@@ -147,13 +375,22 @@ async function useBrand(
 
   for (const fileToCopy of filesToCopy) {
     const isDir = Deno.statSync(fileToCopy).isDirectory;
-    const rel = relative(stagedDir, fileToCopy);
     if (isDir) {
       continue;
     }
+
+    // Compute target path relative to brand file's directory
+    // The brand file itself is renamed to _brand.yml
+    let targetRel: string;
+    if (fileToCopy === brandFilePath) {
+      targetRel = "_brand.yml";
+    } else {
+      targetRel = relative(brandFileDir, fileToCopy);
+    }
+
     // Compute the paths
-    const targetPath = join(brandDir, rel);
-    const displayName = rel;
+    const targetPath = join(brandDir, targetRel);
+    const displayName = targetRel;
     const targetDir = dirname(targetPath);
     const copyAction = {
       file: displayName,
@@ -387,10 +624,10 @@ async function ensureBrandDirectory(force: boolean, dryRun: boolean) {
   const currentDir = Deno.cwd();
   const nbContext = notebookContext();
   const project = await projectContext(currentDir, nbContext);
-  if (!project) {
-    throw new Error(`Could not find project dir for ${currentDir}`);
-  }
-  const brandDir = join(project.dir, "_brand");
+  // Use project directory if available, otherwise fall back to current directory
+  // (single-file mode without _quarto.yml)
+  const baseDir = project?.dir ?? currentDir;
+  const brandDir = join(baseDir, "_brand");
   if (!existsSync(brandDir)) {
     if (dryRun) {
       info(`  Would create directory: _brand/`);
diff --git a/tests/smoke/use-brand/basic-brand/README.md b/tests/smoke/use-brand/basic-brand/README.md
new file mode 100644
index 00000000000..7a93756e12c
--- /dev/null
+++ b/tests/smoke/use-brand/basic-brand/README.md
@@ -0,0 +1,3 @@
+# Basic Brand
+
+This README should not be copied.
diff --git a/tests/smoke/use-brand/basic-brand/_brand.yml b/tests/smoke/use-brand/basic-brand/_brand.yml
index 52e42199215..52e295ad3a4 100644
--- a/tests/smoke/use-brand/basic-brand/_brand.yml
+++ b/tests/smoke/use-brand/basic-brand/_brand.yml
@@ -2,3 +2,11 @@ meta:
   name: Basic Test Brand
 color:
   primary: "#007bff"
+logo:
+  small: logo.png
+typography:
+  fonts:
+    - source: file
+      family: "Custom Font"
+      files:
+        - fonts/custom-font.woff2
diff --git a/tests/smoke/use-brand/basic-brand/fonts/custom-font.woff2 b/tests/smoke/use-brand/basic-brand/fonts/custom-font.woff2
new file mode 100644
index 00000000000..afa17bb7b02
--- /dev/null
+++ b/tests/smoke/use-brand/basic-brand/fonts/custom-font.woff2
@@ -0,0 +1 @@
+DUMMY WOFF2 FONT
diff --git a/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/_extension.yml b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/_extension.yml
new file mode 100644
index 00000000000..27ce469ea66
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/_extension.yml
@@ -0,0 +1,8 @@
+title: Test Brand Extension with Subdir
+author: Test Author
+version: 1.0.0
+quarto-required: ">=1.4.0"
+contributes:
+  metadata:
+    project:
+      brand: subdir/brand.yml
diff --git a/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/brand.yml b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/brand.yml
new file mode 100644
index 00000000000..b1051680f92
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/brand.yml
@@ -0,0 +1,7 @@
+meta:
+  name: Test Brand Extension Subdir
+color:
+  primary: "#ff5733"
+logo:
+  small: logo.png
+  medium: images/nested-logo.png
diff --git a/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/images/nested-logo.png b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/images/nested-logo.png
new file mode 100644
index 00000000000..a15bb813d9c
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/images/nested-logo.png
@@ -0,0 +1 @@
+NESTED LOGO PNG
diff --git a/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/logo.png b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/logo.png
new file mode 100644
index 00000000000..0f5879fc5c8
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension-subdir/_extensions/test-org/test-brand/subdir/logo.png
@@ -0,0 +1 @@
+SUBDIR LOGO PNG
diff --git a/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/_extension.yml b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/_extension.yml
new file mode 100644
index 00000000000..30faf6b6004
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/_extension.yml
@@ -0,0 +1,8 @@
+title: Test Brand Extension
+author: Test Author
+version: 1.0.0
+quarto-required: ">=1.4.0"
+contributes:
+  metadata:
+    project:
+      brand: brand.yml
diff --git a/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/brand.yml b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/brand.yml
new file mode 100644
index 00000000000..9a6aff311c3
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/brand.yml
@@ -0,0 +1,10 @@
+meta:
+  name: Test Brand Extension
+color:
+  primary: "#007bff"
+  secondary: "#6c757d"
+logo:
+  images:
+    brand:
+      path: logo.png
+      alt: "Brand extension logo"
diff --git a/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/logo.png b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/logo.png
new file mode 100644
index 00000000000..c8ba37dd5c9
Binary files /dev/null and b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/logo.png differ
diff --git a/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/template.html b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/template.html
new file mode 100644
index 00000000000..35fa31f0578
--- /dev/null
+++ b/tests/smoke/use-brand/brand-extension/_extensions/test-org/test-brand/template.html
@@ -0,0 +1 @@
+Template file that should not be copied
diff --git a/tests/smoke/use-brand/multi-file-brand/_brand.yml b/tests/smoke/use-brand/multi-file-brand/_brand.yml
index 11c1107b45f..9a5479db1a4 100644
--- a/tests/smoke/use-brand/multi-file-brand/_brand.yml
+++ b/tests/smoke/use-brand/multi-file-brand/_brand.yml
@@ -2,3 +2,22 @@ meta:
   name: Multi-file Test Brand
 color:
   primary: "#28a745"
+logo:
+  images:
+    main:
+      path: logo.png
+      alt: "Main logo"
+    favicon:
+      path: favicon.png
+      alt: "Favicon"
+typography:
+  fonts:
+    - source: file
+      family: "Brand Font"
+      files:
+        - path: fonts/brand-regular.woff2
+          weight: 400
+          style: normal
+        - path: fonts/brand-bold.woff2
+          weight: 700
+          style: normal
diff --git a/tests/smoke/use-brand/multi-file-brand/fonts/brand-bold.woff2 b/tests/smoke/use-brand/multi-file-brand/fonts/brand-bold.woff2
new file mode 100644
index 00000000000..b37a14af8a1
--- /dev/null
+++ b/tests/smoke/use-brand/multi-file-brand/fonts/brand-bold.woff2
@@ -0,0 +1 @@
+DUMMY BOLD FONT
diff --git a/tests/smoke/use-brand/multi-file-brand/fonts/brand-regular.woff2 b/tests/smoke/use-brand/multi-file-brand/fonts/brand-regular.woff2
new file mode 100644
index 00000000000..b6cb50f7527
--- /dev/null
+++ b/tests/smoke/use-brand/multi-file-brand/fonts/brand-regular.woff2
@@ -0,0 +1 @@
+DUMMY REGULAR FONT
diff --git a/tests/smoke/use-brand/multi-file-brand/fonts/unused-italic.woff2 b/tests/smoke/use-brand/multi-file-brand/fonts/unused-italic.woff2
new file mode 100644
index 00000000000..a1349dc1a9b
--- /dev/null
+++ b/tests/smoke/use-brand/multi-file-brand/fonts/unused-italic.woff2
@@ -0,0 +1 @@
+DUMMY UNUSED FONT
diff --git a/tests/smoke/use-brand/multi-file-brand/unused-styles.css b/tests/smoke/use-brand/multi-file-brand/unused-styles.css
new file mode 100644
index 00000000000..9b6ff8e34de
--- /dev/null
+++ b/tests/smoke/use-brand/multi-file-brand/unused-styles.css
@@ -0,0 +1,2 @@
+/* Unreferenced styles */
+.unused { color: red; }
diff --git a/tests/smoke/use-brand/nested-brand/_brand.yml b/tests/smoke/use-brand/nested-brand/_brand.yml
index 345aa0e4b15..4651b5d5e61 100644
--- a/tests/smoke/use-brand/nested-brand/_brand.yml
+++ b/tests/smoke/use-brand/nested-brand/_brand.yml
@@ -2,3 +2,7 @@ meta:
   name: Nested Test Brand
 color:
   primary: "#dc3545"
+logo:
+  small:
+    light: images/logo.png
+    dark: images/header.png
diff --git a/tests/smoke/use-brand/nested-brand/images/extra-icon.png b/tests/smoke/use-brand/nested-brand/images/extra-icon.png
new file mode 100644
index 00000000000..52b425a5471
--- /dev/null
+++ b/tests/smoke/use-brand/nested-brand/images/extra-icon.png
@@ -0,0 +1 @@
+Extra unreferenced image placeholder
diff --git a/tests/smoke/use-brand/nested-brand/notes.txt b/tests/smoke/use-brand/nested-brand/notes.txt
new file mode 100644
index 00000000000..78b0632209b
--- /dev/null
+++ b/tests/smoke/use-brand/nested-brand/notes.txt
@@ -0,0 +1 @@
+Unreferenced notes file
diff --git a/tests/smoke/use/brand.test.ts b/tests/smoke/use/brand.test.ts
index 766f26ca410..1e21348674d 100644
--- a/tests/smoke/use/brand.test.ts
+++ b/tests/smoke/use/brand.test.ts
@@ -74,6 +74,19 @@ testQuartoCmd(
     folderExists(join(basicDir, "_brand")),
     fileExists(join(basicDir, "_brand", "_brand.yml")),
     fileExists(join(basicDir, "_brand", "logo.png")),
+    // Font file referenced in typography.fonts should be copied
+    folderExists(join(basicDir, "_brand", "fonts")),
+    fileExists(join(basicDir, "_brand", "fonts", "custom-font.woff2")),
+    // README.md is NOT referenced in _brand.yml - should NOT be copied
+    {
+      name: "README.md should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(basicDir, "_brand", "README.md"))) {
+          throw new Error("README.md should not be copied - it is not referenced in _brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
   ],
   {
     setup: () => {
@@ -98,7 +111,7 @@ testQuartoCmd(
   [
     noErrorsOrWarnings,
     printsMessage({ level: "INFO", regex: /Would create directory/ }),
-    filesInSections({ create: ["_brand.yml", "logo.png"] }, true),
+    filesInSections({ create: ["_brand.yml", "logo.png", "fonts/custom-font.woff2"] }, true),
     {
       name: "_brand directory should not exist in dry-run mode",
       verify: () => {
@@ -108,7 +121,19 @@ testQuartoCmd(
         }
         return Promise.resolve();
       }
-    }
+    },
+    // README.md should NOT appear in dry-run output (unreferenced)
+    {
+      name: "README.md should not be listed in dry-run output (unreferenced)",
+      verify: (outputs: ExecuteOutput[]) => {
+        for (const output of outputs) {
+          if (output.msg.includes("README.md")) {
+            throw new Error("README.md should not appear in dry-run output - it is not referenced in _brand.yml");
+          }
+        }
+        return Promise.resolve();
+      }
+    },
   ],
   {
     setup: () => {
@@ -284,6 +309,30 @@ testQuartoCmd(
     fileExists(join(multiFileDir, "_brand", "_brand.yml")),
     fileExists(join(multiFileDir, "_brand", "logo.png")),
     fileExists(join(multiFileDir, "_brand", "favicon.png")),
+    // Font files referenced in typography.fonts should be copied
+    folderExists(join(multiFileDir, "_brand", "fonts")),
+    fileExists(join(multiFileDir, "_brand", "fonts", "brand-regular.woff2")),
+    fileExists(join(multiFileDir, "_brand", "fonts", "brand-bold.woff2")),
+    // unused-styles.css is NOT referenced in _brand.yml - should NOT be copied
+    {
+      name: "unused-styles.css should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(multiFileDir, "_brand", "unused-styles.css"))) {
+          throw new Error("unused-styles.css should not be copied - it is not referenced in _brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
+    // fonts/unused-italic.woff2 is NOT referenced in _brand.yml - should NOT be copied
+    {
+      name: "fonts/unused-italic.woff2 should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(multiFileDir, "_brand", "fonts", "unused-italic.woff2"))) {
+          throw new Error("fonts/unused-italic.woff2 should not be copied - it is not referenced in _brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
   ],
   {
     setup: () => {
@@ -312,6 +361,26 @@ testQuartoCmd(
     folderExists(join(nestedDir, "_brand", "images")),
     fileExists(join(nestedDir, "_brand", "images", "logo.png")),
     fileExists(join(nestedDir, "_brand", "images", "header.png")),
+    // notes.txt is NOT referenced in _brand.yml - should NOT be copied
+    {
+      name: "notes.txt should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(nestedDir, "_brand", "notes.txt"))) {
+          throw new Error("notes.txt should not be copied - it is not referenced in _brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
+    // images/extra-icon.png is NOT referenced in _brand.yml - should NOT be copied
+    {
+      name: "images/extra-icon.png should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(nestedDir, "_brand", "images", "extra-icon.png"))) {
+          throw new Error("images/extra-icon.png should not be copied - it is not referenced in _brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
   ],
   {
     setup: () => {
@@ -327,18 +396,22 @@ testQuartoCmd(
   "quarto use brand - nested directory structure"
 );
 
-// Scenario 8: Error - no project directory
+// Scenario 8: Single-file mode (no _quarto.yml) - should work, using current directory
 const noProjectDir = join(tempDir, "no-project");
 ensureDirSync(noProjectDir);
 testQuartoCmd(
   "use",
   ["brand", join(fixtureDir, "basic-brand"), "--force"],
   [
-    printsMessage({ level: "ERROR", regex: /Could not find project dir/ }),
+    noErrorsOrWarnings,
+    // Should create _brand/ in the current directory even without _quarto.yml
+    folderExists(join(noProjectDir, "_brand")),
+    fileExists(join(noProjectDir, "_brand", "_brand.yml")),
+    fileExists(join(noProjectDir, "_brand", "logo.png")),
   ],
   {
     setup: () => {
-      // No _quarto.yml created - this should cause an error
+      // No _quarto.yml created - single-file mode should work
       return Promise.resolve();
     },
     cwd: () => noProjectDir,
@@ -347,7 +420,7 @@ testQuartoCmd(
       return Promise.resolve();
     }
   },
-  "quarto use brand - error on no project"
+  "quarto use brand - single-file mode (no _quarto.yml)"
 );
 
 // Scenario 9: Nested directory - overwrite files in subdirectories, remove extra
@@ -650,3 +723,144 @@ testQuartoCmd(
   },
   "quarto use brand - deeply nested directories recursively cleaned up"
 );
+
+// Scenario 15: Brand extension - basic installation
+// Tests that brand extensions are detected and the brand file is renamed to _brand.yml
+const brandExtDir = join(tempDir, "brand-ext");
+ensureDirSync(brandExtDir);
+testQuartoCmd(
+  "use",
+  ["brand", join(fixtureDir, "brand-extension"), "--force"],
+  [
+    noErrorsOrWarnings,
+    folderExists(join(brandExtDir, "_brand")),
+    // brand.yml should be renamed to _brand.yml
+    fileExists(join(brandExtDir, "_brand", "_brand.yml")),
+    // logo.png should be copied
+    fileExists(join(brandExtDir, "_brand", "logo.png")),
+    // _extension.yml should NOT be copied
+    {
+      name: "_extension.yml should not be copied",
+      verify: () => {
+        if (existsSync(join(brandExtDir, "_brand", "_extension.yml"))) {
+          throw new Error("_extension.yml should not be copied from brand extension");
+        }
+        return Promise.resolve();
+      }
+    },
+    // Verify the content is correct (from brand.yml, not some other file)
+    {
+      name: "_brand.yml should contain brand extension content",
+      verify: () => {
+        const content = Deno.readTextFileSync(join(brandExtDir, "_brand", "_brand.yml"));
+        if (!content.includes("Test Brand Extension")) {
+          throw new Error("_brand.yml should contain content from brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
+    // template.html is NOT referenced in brand.yml - should NOT be copied
+    {
+      name: "template.html should not be copied (unreferenced)",
+      verify: () => {
+        if (existsSync(join(brandExtDir, "_brand", "template.html"))) {
+          throw new Error("template.html should not be copied - it is not referenced in brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
+  ],
+  {
+    setup: () => {
+      Deno.writeTextFileSync(join(brandExtDir, "_quarto.yml"), "project:\n  type: default\n");
+      return Promise.resolve();
+    },
+    cwd: () => brandExtDir,
+    teardown: () => {
+      try { Deno.removeSync(brandExtDir, { recursive: true }); } catch { /* ignore */ }
+      return Promise.resolve();
+    }
+  },
+  "quarto use brand - brand extension installation"
+);
+
+// Scenario 16: Brand extension - dry-run shows correct file names
+const brandExtDryRunDir = join(tempDir, "brand-ext-dry-run");
+ensureDirSync(brandExtDryRunDir);
+testQuartoCmd(
+  "use",
+  ["brand", join(fixtureDir, "brand-extension"), "--dry-run"],
+  [
+    noErrorsOrWarnings,
+    // Should show _brand.yml (renamed from brand.yml), not brand.yml
+    filesInSections({ create: ["_brand.yml", "logo.png"] }, true),
+    // _brand directory should not exist in dry-run mode
+    {
+      name: "_brand directory should not exist in dry-run mode",
+      verify: () => {
+        if (existsSync(join(brandExtDryRunDir, "_brand"))) {
+          throw new Error("_brand directory should not exist in dry-run mode");
+        }
+        return Promise.resolve();
+      }
+    }
+  ],
+  {
+    setup: () => {
+      Deno.writeTextFileSync(join(brandExtDryRunDir, "_quarto.yml"), "project:\n  type: default\n");
+      return Promise.resolve();
+    },
+    cwd: () => brandExtDryRunDir,
+    teardown: () => {
+      try { Deno.removeSync(brandExtDryRunDir, { recursive: true }); } catch { /* ignore */ }
+      return Promise.resolve();
+    }
+  },
+  "quarto use brand - brand extension dry-run shows renamed file"
+);
+
+// Scenario 17: Brand extension with brand file in subdirectory
+// Tests that brand path in _extension.yml can be a relative path (e.g., subdir/brand.yml)
+// and that referenced files are resolved relative to the brand file's directory
+const brandExtSubdirDir = join(tempDir, "brand-ext-subdir");
+ensureDirSync(brandExtSubdirDir);
+testQuartoCmd(
+  "use",
+  ["brand", join(fixtureDir, "brand-extension-subdir"), "--force"],
+  [
+    noErrorsOrWarnings,
+    folderExists(join(brandExtSubdirDir, "_brand")),
+    // subdir/brand.yml should be renamed to _brand.yml
+    fileExists(join(brandExtSubdirDir, "_brand", "_brand.yml")),
+    // logo.png (referenced as logo.png in subdir/brand.yml) should be copied
+    // The logo is at subdir/logo.png relative to extension dir
+    fileExists(join(brandExtSubdirDir, "_brand", "logo.png")),
+    // images/nested-logo.png (referenced as images/nested-logo.png in subdir/brand.yml)
+    // should be copied to _brand/images/nested-logo.png
+    folderExists(join(brandExtSubdirDir, "_brand", "images")),
+    fileExists(join(brandExtSubdirDir, "_brand", "images", "nested-logo.png")),
+    // Verify the content is correct
+    {
+      name: "_brand.yml should contain subdir brand content",
+      verify: () => {
+        const content = Deno.readTextFileSync(join(brandExtSubdirDir, "_brand", "_brand.yml"));
+        if (!content.includes("Test Brand Extension Subdir")) {
+          throw new Error("_brand.yml should contain content from subdir/brand.yml");
+        }
+        return Promise.resolve();
+      }
+    },
+  ],
+  {
+    setup: () => {
+      Deno.writeTextFileSync(join(brandExtSubdirDir, "_quarto.yml"), "project:\n  type: default\n");
+      return Promise.resolve();
+    },
+    cwd: () => brandExtSubdirDir,
+    teardown: () => {
+      try { Deno.removeSync(brandExtSubdirDir, { recursive: true }); } catch { /* ignore */ }
+      return Promise.resolve();
+    }
+  },
+  "quarto use brand - brand extension with subdir brand file"
+);