diff --git a/packages/@apphosting/adapter-nextjs/src/bin/build.spec.ts b/packages/@apphosting/adapter-nextjs/src/bin/build.spec.ts
index 8fb1177f..bae61c33 100644
--- a/packages/@apphosting/adapter-nextjs/src/bin/build.spec.ts
+++ b/packages/@apphosting/adapter-nextjs/src/bin/build.spec.ts
@@ -164,6 +164,112 @@ outputFiles:
       async () => await validateOutputDirectory(outputBundleOptions, path.join(tmpDir, ".next")),
     );
   });
+  it(".apphosting gitignored correctly in a monorepo setup", async () => {
+    const { generateBuildOutput } = await importUtils;
+    const files = {
+      ".next/standalone/apps/next-app/standalonefile": "",
+      ".next/static/staticfile": "",
+    };
+    generateTestFiles(tmpDir, files);
+    await generateBuildOutput(
+      tmpDir,
+      "apps/next-app",
+      {
+        bundleYamlPath: path.join(tmpDir, ".apphosting", "bundle.yaml"),
+        outputDirectoryBasePath: path.join(tmpDir, ".apphosting"),
+        outputDirectoryAppPath: path.join(tmpDir, ".next", "standalone", "apps", "next-app"),
+        outputPublicDirectoryPath: path.join(
+          tmpDir,
+          ".next",
+          "standalone",
+          "apps",
+          "next-app",
+          "public",
+        ),
+        outputStaticDirectoryPath: path.join(
+          tmpDir,
+          ".next",
+          "standalone",
+          "apps",
+          "next-app",
+          ".next",
+          "static",
+        ),
+        serverFilePath: path.join(tmpDir, ".next", "standalone", "apps", "next-app", "server.js"),
+      },
+      path.join(tmpDir, ".next"),
+      defaultNextVersion,
+      adapterMetadata,
+    );
+
+    const expectedFiles = {
+      ".gitignore": "/.apphosting/",
+    };
+    const expectedPartialYaml = {
+      version: "v1",
+      runConfig: { runCommand: "node .next/standalone/apps/next-app/server.js" },
+    };
+    validateTestFiles(tmpDir, expectedFiles);
+    validatePartialYamlContents(tmpDir, ".apphosting/bundle.yaml", expectedPartialYaml);
+  });
+
+  it(".apphosting gitignored without existing .gitignore file", async () => {
+    const { generateBuildOutput, validateOutputDirectory } = await importUtils;
+    const files = {
+      // .next/standalone/.next/ must be created beforehand otherwise
+      // generateBuildOutput will attempt to copy
+      // .next/ into .next/standalone/.next
+      ".next/standalone/.next/package.json": "",
+      ".next/static/staticfile": "",
+    };
+    generateTestFiles(tmpDir, files);
+    await generateBuildOutput(
+      tmpDir,
+      tmpDir,
+      outputBundleOptions,
+      path.join(tmpDir, ".next"),
+      defaultNextVersion,
+      {
+        adapterPackageName: "@apphosting/adapter-nextjs",
+        adapterVersion: "14.0.1",
+      },
+    );
+    await validateOutputDirectory(outputBundleOptions, path.join(tmpDir, ".next"));
+
+    const expectedFiles = {
+      ".gitignore": "/.apphosting/",
+    };
+    validateTestFiles(tmpDir, expectedFiles);
+  });
+  it(".apphosting gitignored in existing .gitignore file", async () => {
+    const { generateBuildOutput, validateOutputDirectory } = await importUtils;
+    const files = {
+      // .next/standalone/.next/ must be created beforehand otherwise
+      // generateBuildOutput will attempt to copy
+      // .next/ into .next/standalone/.next
+      ".next/standalone/.next/package.json": "",
+      ".next/static/staticfile": "",
+      ".gitignore": "/.next/",
+    };
+    generateTestFiles(tmpDir, files);
+    await generateBuildOutput(
+      tmpDir,
+      tmpDir,
+      outputBundleOptions,
+      path.join(tmpDir, ".next"),
+      defaultNextVersion,
+      {
+        adapterPackageName: "@apphosting/adapter-nextjs",
+        adapterVersion: "14.0.1",
+      },
+    );
+    await validateOutputDirectory(outputBundleOptions, path.join(tmpDir, ".next"));
+
+    const expectedFiles = {
+      ".gitignore": "/.next/\n/.apphosting/",
+    };
+    validateTestFiles(tmpDir, expectedFiles);
+  });
   it("expects directories and other files to be copied over", async () => {
     const { generateBuildOutput, validateOutputDirectory } = await importUtils;
     const files = {
diff --git a/packages/@apphosting/adapter-nextjs/src/utils.ts b/packages/@apphosting/adapter-nextjs/src/utils.ts
index ed6cbc0a..ed92422b 100644
--- a/packages/@apphosting/adapter-nextjs/src/utils.ts
+++ b/packages/@apphosting/adapter-nextjs/src/utils.ts
@@ -12,10 +12,10 @@ import {
   MiddlewareManifest,
 } from "./interfaces.js";
 import { NextConfigComplete } from "next/dist/server/config-shared.js";
-import { OutputBundleConfig } from "@apphosting/common";
+import { OutputBundleConfig, updateOrCreateGitignore } from "@apphosting/common";
 
 // fs-extra is CJS, readJson can't be imported using shorthand
-export const { copy, exists, writeFile, readJson, readdir, readFileSync, existsSync, mkdir } =
+export const { copy, exists, writeFile, readJson, readdir, readFileSync, existsSync, ensureDir } =
   fsExtra;
 
 // Loads the user's next.config.js file.
@@ -181,7 +181,7 @@ async function generateBundleYaml(
   nextVersion: string,
   adapterMetadata: AdapterMetadata,
 ): Promise<void> {
-  await mkdir(opts.outputDirectoryBasePath);
+  await ensureDir(opts.outputDirectoryBasePath);
   const outputBundle: OutputBundleConfig = {
     version: "v1",
     runConfig: {
@@ -203,6 +203,8 @@ async function generateBundleYaml(
   }
 
   await writeFile(opts.bundleYamlPath, yamlStringify(outputBundle));
+  const normalizedBundleDir = normalize(relative(cwd, opts.outputDirectoryBasePath));
+  updateOrCreateGitignore(cwd, [`/${normalizedBundleDir}/`]);
   return;
 }
 
diff --git a/packages/@apphosting/common/package.json b/packages/@apphosting/common/package.json
index 25ae288e..ed144d7b 100644
--- a/packages/@apphosting/common/package.json
+++ b/packages/@apphosting/common/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@apphosting/common",
-  "version": "0.0.5",
+  "version": "0.0.6",
   "description": "Shared library code for App Hosting framework adapters",
   "author": {
     "name": "Firebase",
@@ -17,6 +17,7 @@
   },
   "scripts": {
     "build": "tsc",
+    "test": "ts-mocha -p tsconfig.json 'src/**/*.spec.ts' 'src/*.spec.ts'",
     "localregistry:start": "npx verdaccio --config ../publish-dev/verdaccio-config.yaml",
     "localregistry:publish": "(npm view --registry=http://localhost:4873 @apphosting/common && npm unpublish --@apphosting:registry=http://localhost:4873 --force); npm publish --@apphosting:registry=http://localhost:4873"
   },
diff --git a/packages/@apphosting/common/src/index.spec.ts b/packages/@apphosting/common/src/index.spec.ts
new file mode 100644
index 00000000..27bdbd57
--- /dev/null
+++ b/packages/@apphosting/common/src/index.spec.ts
@@ -0,0 +1,30 @@
+import assert from "assert";
+import fs from "fs";
+import path from "path";
+import os from "os";
+import { updateOrCreateGitignore } from "./index";
+
+describe("update or create .gitignore", () => {
+  let tmpDir: string;
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "test-gitignore"));
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it(".gitignore file exists and is correctly updated with missing paths", () => {
+    fs.writeFileSync(path.join(tmpDir, ".gitignore"), "existingpath/");
+
+    updateOrCreateGitignore(tmpDir, ["existingpath/", "newpath/"]);
+
+    const gitignoreContent = fs.readFileSync(path.join(tmpDir, ".gitignore"), "utf-8");
+    assert.equal(`existingpath/\nnewpath/`, gitignoreContent);
+  });
+  it(".gitignore file does not exist and is created", () => {
+    updateOrCreateGitignore(tmpDir, ["chickenpath/", "newpath/"]);
+    const gitignoreContent = fs.readFileSync(path.join(tmpDir, ".gitignore"), "utf-8");
+    assert.equal(`chickenpath/\nnewpath/`, gitignoreContent);
+  });
+});
diff --git a/packages/@apphosting/common/src/index.ts b/packages/@apphosting/common/src/index.ts
index 6319a0cc..f16d32db 100644
--- a/packages/@apphosting/common/src/index.ts
+++ b/packages/@apphosting/common/src/index.ts
@@ -1,4 +1,6 @@
 import { spawn } from "child_process";
+import * as fs from "node:fs";
+import * as path from "node:path";
 
 // Output bundle metadata specifications to be written to bundle.yaml
 export interface OutputBundleConfig {
@@ -139,3 +141,26 @@ export function getBuildOptions(): BuildOptions {
     projectDirectory: process.cwd(),
   };
 }
+
+/**
+ * Updates or creates a .gitignore file with the given entries in the given path
+ */
+export function updateOrCreateGitignore(dirPath: string, entries: string[]) {
+  const gitignorePath = path.join(dirPath, ".gitignore");
+
+  if (!fs.existsSync(gitignorePath)) {
+    console.log(`creating ${gitignorePath} with entries: ${entries.join("\n")}`);
+    fs.writeFileSync(gitignorePath, entries.join("\n"));
+    return;
+  }
+
+  let content = fs.readFileSync(gitignorePath, "utf-8");
+  for (const entry of entries) {
+    if (!content.split("\n").includes(entry)) {
+      console.log(`adding ${entry} to ${gitignorePath}`);
+      content += `\n${entry}`;
+    }
+  }
+
+  fs.writeFileSync(gitignorePath, content);
+}