diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 229fc486b..2ccbcfacb 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -261,6 +261,11 @@ useEffect(
 
 This version updates the TypeScript parser to correctly handle JSX text with double slashes (`//`). In previous versions, this would cause Prettier to crash.
 
+#### CLI: Add `--only-changed` flag ([#5910] by [@g-harel])
+
+Flag used with `--write` to avoid re-checking files that were not changed since they were last written (with the same formatting configuration).
+
+[#5910]: https://github.com/prettier/prettier/pull/5910
 [#6186]: https://github.com/prettier/prettier/pull/6186
 [#6206]: https://github.com/prettier/prettier/pull/6206
 [#6209]: https://github.com/prettier/prettier/pull/6209
@@ -272,3 +277,4 @@ This version updates the TypeScript parser to correctly handle JSX text with dou
 [@duailibe]: https://github.com/duailibe
 [@gavinjoyce]: https://github.com/gavinjoyce
 [@sosukesuzuki]: https://github.com/sosukesuzuki
+[@g-harel]: https://github.com/g-harel
diff --git a/docs/cli.md b/docs/cli.md
index 5dab730fc..d5a94ec7f 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -148,6 +148,8 @@ Prettier CLI will ignore files located in `node_modules` directory. To opt-out f
 
 This rewrites all processed files in place. This is comparable to the `eslint --fix` workflow.
 
+To avoid re-checking unchanged files, use the `--only-changed` flag.
+
 ## `--loglevel`
 
 Change the level of logging for the CLI. Valid options are:
diff --git a/package.json b/package.json
index 509f8b9e4..11d2bbfbd 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
     "editorconfig-to-prettier": "0.1.1",
     "escape-string-regexp": "1.0.5",
     "esutils": "2.0.2",
+    "find-cache-dir": "1.0.0",
     "find-parent-dir": "0.3.0",
     "find-project-root": "1.1.1",
     "flow-parser": "0.84.0",
@@ -71,6 +72,7 @@
     "unicode-regex": "2.0.0",
     "unified": "6.1.6",
     "vnopts": "1.0.2",
+    "write-file-atomic": "2.3.0",
     "yaml": "1.0.2",
     "yaml-unist-parser": "1.0.0"
   },
diff --git a/src/cli/changed-cache.js b/src/cli/changed-cache.js
new file mode 100644
index 000000000..abb377e79
--- /dev/null
+++ b/src/cli/changed-cache.js
@@ -0,0 +1,79 @@
+"use strict";
+
+const crypto = require("crypto");
+
+// Generates a hash of the input string.
+function hash(data) {
+  return crypto
+    .createHash("sha1")
+    .update(data)
+    .digest("base64");
+}
+
+// Generates the cache key using the file path, options and the support info hash.
+function calcKey(path, options, supportInfoHash) {
+  return hash(path + JSON.stringify(options) + supportInfoHash);
+}
+
+class ChangedCache {
+  // Initializes the in-memory cache data from the configured location.
+  // Also calculates the static support info hash used to compute file keys.
+  // A missing cache file is not treated as an error because it is expected on first run.
+  constructor(options) {
+    this.location = options.location;
+    this.readFile = options.readFile;
+    this.writeFile = options.writeFile;
+    this.context = options.context;
+    this.supportInfoHash = hash(JSON.stringify(options.supportInfo));
+
+    this.cache = {};
+
+    let contents;
+    try {
+      contents = this.readFile(this.location, "utf8");
+    } catch (err) {
+      if (err.code !== "ENOENT") {
+        this.context.logger.error(`Could not read cache file: ${err}`);
+      }
+      return;
+    }
+
+    try {
+      this.cache = JSON.parse(contents);
+    } catch (err) {
+      this.context.logger.error(`Could not parse cache contents: ${err}`);
+    }
+  }
+
+  // Writes the in-memory cache data to the configured file.
+  // Previous file contents are overwritten.
+  close() {
+    let contents;
+    try {
+      contents = JSON.stringify(this.cache);
+    } catch (err) {
+      this.context.logger.error(`Could not serialize cache: ${err}`);
+      return;
+    }
+
+    try {
+      this.writeFile(this.location, contents, "utf8");
+    } catch (err) {
+      this.context.logger.error(`Could not write cache to file: ${err}`);
+    }
+  }
+
+  // Checks if the expected contents of the file path match the in-memory data.
+  notChanged(path, options, content) {
+    return (
+      this.cache[calcKey(path, options, this.supportInfoHash)] === hash(content)
+    );
+  }
+
+  // Updates the expected contents of the file path in the in-memory data.
+  update(path, options, content) {
+    this.cache[calcKey(path, options, this.supportInfoHash)] = hash(content);
+  }
+}
+
+module.exports = ChangedCache;
diff --git a/src/cli/constant.js b/src/cli/constant.js
index 05f7047fe..be4175a97 100644
--- a/src/cli/constant.js
+++ b/src/cli/constant.js
@@ -187,6 +187,10 @@ const options = {
     default: "log",
     choices: ["silent", "error", "warn", "log", "debug"]
   },
+  "only-changed": {
+    type: "boolean",
+    description: "Only format files changed since last '--write'."
+  },
   stdin: {
     type: "boolean",
     description: "Force reading input from stdin."
diff --git a/src/cli/index.js b/src/cli/index.js
index f7a6b7832..9ffd63e45 100644
--- a/src/cli/index.js
+++ b/src/cli/index.js
@@ -22,6 +22,11 @@ function run(args) {
       process.exit(1);
     }
 
+    if (context.argv["only-changed"] && !context.argv["write"]) {
+      context.logger.error("Cannot use --only-changed without --write.");
+      process.exit(1);
+    }
+
     if (context.argv["find-config-path"] && context.filePatterns.length) {
       context.logger.error("Cannot use --find-config-path with multiple files");
       process.exit(1);
diff --git a/src/cli/util.js b/src/cli/util.js
index 592575c00..86d7f6cb8 100644
--- a/src/cli/util.js
+++ b/src/cli/util.js
@@ -8,6 +8,7 @@ const globby = require("globby");
 const chalk = require("chalk");
 const readline = require("readline");
 const stringify = require("json-stable-stringify");
+const findCacheDir = require("find-cache-dir");
 
 const minimist = require("./minimist");
 const prettier = require("../../index");
@@ -20,6 +21,7 @@ const optionsNormalizer = require("../main/options-normalizer");
 const thirdParty = require("../common/third-party");
 const arrayify = require("../utils/arrayify");
 const isTTY = require("../utils/is-tty");
+const ChangedCache = require("./changed-cache");
 
 const OPTION_USAGE_THRESHOLD = 25;
 const CHOICE_USAGE_MARGIN = 3;
@@ -441,6 +443,18 @@ function formatFiles(context) {
     context.logger.log("Checking formatting...");
   }
 
+  let changedCache = null;
+  if (context.argv["only-changed"]) {
+    const cacheDir = findCacheDir({ name: "prettier", create: true });
+    changedCache = new ChangedCache({
+      location: path.join(cacheDir, "changed"),
+      readFile: fs.readFileSync,
+      writeFile: thirdParty.writeFileAtomic,
+      context: context,
+      supportInfo: prettier.getSupportInfo()
+    });
+  }
+
   eachFilename(context, context.filePatterns, filename => {
     const fileIgnored = ignorer.filter([filename]).length === 0;
     if (
@@ -457,9 +471,15 @@ function formatFiles(context) {
       filepath: filename
     });
 
+    let removeFilename = () => {};
     if (isTTY()) {
       // Don't use `console.log` here since we need to replace this line.
       context.logger.log(filename, { newline: false });
+      removeFilename = () => {
+        readline.clearLine(process.stdout, 0);
+        readline.cursorTo(process.stdout, 0, null);
+        removeFilename = () => {};
+      };
     }
 
     let input;
@@ -477,6 +497,19 @@ function formatFiles(context) {
       return;
     }
 
+    if (changedCache) {
+      if (changedCache.notChanged(filename, options, input)) {
+        // Remove previously printed filename to log it with "unchanged".
+        removeFilename();
+
+        if (!context.argv["check"] && !context.argv["list-different"]) {
+          context.logger.log(chalk.grey(`${filename} unchanged`));
+        }
+
+        return;
+      }
+    }
+
     if (fileIgnored) {
       writeOutput(context, { formatted: input }, options);
       return;
@@ -501,11 +534,8 @@ function formatFiles(context) {
 
     const isDifferent = output !== input;
 
-    if (isTTY()) {
-      // Remove previously printed filename to log it with duration.
-      readline.clearLine(process.stdout, 0);
-      readline.cursorTo(process.stdout, 0, null);
-    }
+    // Remove previously printed filename to log it with duration.
+    removeFilename();
 
     if (context.argv["write"]) {
       // Don't write the file if it won't change in order not to invalidate
@@ -524,8 +554,15 @@ function formatFiles(context) {
           // Don't exit the process if one file failed
           process.exitCode = 2;
         }
-      } else if (!context.argv["check"] && !context.argv["list-different"]) {
-        context.logger.log(`${chalk.grey(filename)} ${Date.now() - start}ms`);
+      } else {
+        if (!context.argv["check"] && !context.argv["list-different"]) {
+          context.logger.log(`${chalk.grey(filename)} ${Date.now() - start}ms`);
+        }
+      }
+
+      // Cache is updated to record pretty content.
+      if (changedCache) {
+        changedCache.update(filename, options, output);
       }
     } else if (context.argv["debug-check"]) {
       if (result.filepath) {
@@ -546,6 +583,10 @@ function formatFiles(context) {
     }
   });
 
+  if (changedCache) {
+    changedCache.close();
+  }
+
   // Print check summary based on expected exit code
   if (context.argv["check"]) {
     context.logger.log(
diff --git a/src/common/third-party.js b/src/common/third-party.js
index 8089f5fde..570dbbc2d 100644
--- a/src/common/third-party.js
+++ b/src/common/third-party.js
@@ -4,5 +4,6 @@ module.exports = {
   cosmiconfig: require("cosmiconfig"),
   findParentDir: require("find-parent-dir").sync,
   getStream: require("get-stream"),
-  isCI: () => require("is-ci")
+  isCI: () => require("is-ci"),
+  writeFileAtomic: require("write-file-atomic").sync
 };
diff --git a/tests_integration/__tests__/__snapshots__/early-exit.js.snap b/tests_integration/__tests__/__snapshots__/early-exit.js.snap
index 458a18be6..785f2e912 100644
--- a/tests_integration/__tests__/__snapshots__/early-exit.js.snap
+++ b/tests_integration/__tests__/__snapshots__/early-exit.js.snap
@@ -141,6 +141,7 @@ Other options:
   --loglevel <silent|error|warn|log|debug>
                            What level of logs to report.
                            Defaults to log.
+  --only-changed           Only format files changed since last '--write'.
   --require-pragma         Require either '@prettier' or '@format' to be present in the file's first docblock comment
                            in order for it to be formatted.
                            Defaults to false.
@@ -294,6 +295,7 @@ Other options:
   --loglevel <silent|error|warn|log|debug>
                            What level of logs to report.
                            Defaults to log.
+  --only-changed           Only format files changed since last '--write'.
   --require-pragma         Require either '@prettier' or '@format' to be present in the file's first docblock comment
                            in order for it to be formatted.
                            Defaults to false.
@@ -344,6 +346,15 @@ exports[`throw error with --help not-found (stdout) 1`] = `""`;
 
 exports[`throw error with --help not-found (write) 1`] = `Array []`;
 
+exports[`throw error with --only-changed without --write (stderr) 1`] = `
+"[error] Cannot use --only-changed without --write.
+"
+`;
+
+exports[`throw error with --only-changed without --write (stdout) 1`] = `""`;
+
+exports[`throw error with --only-changed without --write (write) 1`] = `Array []`;
+
 exports[`throw error with --write + --debug-check (stderr) 1`] = `
 "[error] Cannot use --write and --debug-check together.
 "
diff --git a/tests_integration/__tests__/__snapshots__/help-options.js.snap b/tests_integration/__tests__/__snapshots__/help-options.js.snap
index 4f43f9fa9..29aaeaeae 100644
--- a/tests_integration/__tests__/__snapshots__/help-options.js.snap
+++ b/tests_integration/__tests__/__snapshots__/help-options.js.snap
@@ -329,6 +329,17 @@ exports[`show detailed usage with --help no-semi (stdout) 1`] = `
 
 exports[`show detailed usage with --help no-semi (write) 1`] = `Array []`;
 
+exports[`show detailed usage with --help only-changed (stderr) 1`] = `""`;
+
+exports[`show detailed usage with --help only-changed (stdout) 1`] = `
+"--only-changed
+
+  Only format files changed since last '--write'.
+"
+`;
+
+exports[`show detailed usage with --help only-changed (write) 1`] = `Array []`;
+
 exports[`show detailed usage with --help parser (stderr) 1`] = `""`;
 
 exports[`show detailed usage with --help parser (stdout) 1`] = `
diff --git a/tests_integration/__tests__/__snapshots__/only-changed.js.snap b/tests_integration/__tests__/__snapshots__/only-changed.js.snap
new file mode 100644
index 000000000..c49c2d715
--- /dev/null
+++ b/tests_integration/__tests__/__snapshots__/only-changed.js.snap
@@ -0,0 +1,43 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`create cache with --write --only-changed + formatted file (stderr) 1`] = `""`;
+
+exports[`create cache with --write --only-changed + formatted file (stdout) 1`] = `
+"formatted.js 0ms
+"
+`;
+
+exports[`create cache with --write --only-changed + unformatted file (stderr) 1`] = `""`;
+
+exports[`create cache with --write --only-changed + unformatted file (stdout) 1`] = `
+"unformatted.js 0ms
+"
+`;
+
+exports[`detect config change with --write --only-changed + unformatted file (stderr) 1`] = `""`;
+
+exports[`detect config change with --write --only-changed + unformatted file (stderr) 2`] = `""`;
+
+exports[`detect config change with --write --only-changed + unformatted file (stdout) 1`] = `
+"unformatted.js 0ms
+"
+`;
+
+exports[`detect config change with --write --only-changed + unformatted file (stdout) 2`] = `
+"unformatted.js 0ms
+"
+`;
+
+exports[`detect unchanged with --write --only-changed + formatted file (stderr) 1`] = `""`;
+
+exports[`detect unchanged with --write --only-changed + formatted file (stderr) 2`] = `""`;
+
+exports[`detect unchanged with --write --only-changed + formatted file (stdout) 1`] = `
+"formatted.js 0ms
+"
+`;
+
+exports[`detect unchanged with --write --only-changed + formatted file (stdout) 2`] = `
+"formatted.js unchanged
+"
+`;
diff --git a/tests_integration/__tests__/early-exit.js b/tests_integration/__tests__/early-exit.js
index 2148eaa74..e0d291b8b 100644
--- a/tests_integration/__tests__/early-exit.js
+++ b/tests_integration/__tests__/early-exit.js
@@ -68,6 +68,12 @@ describe("throw error with --write + --debug-check", () => {
   });
 });
 
+describe("throw error with --only-changed without --write", () => {
+  runPrettier("cli", ["--only-changed"]).test({
+    status: 1
+  });
+});
+
 describe("throw error with --find-config-path + multiple files", () => {
   runPrettier("cli", ["--find-config-path", "abc.js", "def.js"]).test({
     status: 1
diff --git a/tests_integration/__tests__/only-changed.js b/tests_integration/__tests__/only-changed.js
new file mode 100644
index 000000000..e6205b4d4
--- /dev/null
+++ b/tests_integration/__tests__/only-changed.js
@@ -0,0 +1,162 @@
+"use strict";
+
+const path = require("path");
+const findCacheDir = require("find-cache-dir");
+
+const runPrettier = require("../runPrettier");
+const ChangedCache = require("../../src/cli/changed-cache");
+
+// Cache name must be kept consistent with value in the implementation.
+const cacheName = "changed";
+const cachePath = path.join(findCacheDir({ name: "prettier" }), cacheName);
+
+describe("create cache with --write --only-changed + unformatted file", () => {
+  runPrettier("cli/only-changed", [
+    "--write",
+    "--only-changed",
+    "unformatted.js"
+  ]).test({
+    write: [{ filename: "unformatted.js" }, { filename: cachePath }],
+    status: 0
+  });
+});
+
+describe("create cache with --write --only-changed + formatted file", () => {
+  runPrettier("cli/only-changed", [
+    "--write",
+    "--only-changed",
+    "formatted.js"
+  ]).test({
+    write: [{ filename: cachePath }],
+    status: 0
+  });
+});
+
+describe("detect unchanged with --write --only-changed + formatted file", () => {
+  const res = runPrettier("cli/only-changed", [
+    "--write",
+    "--only-changed",
+    "formatted.js"
+  ]).test({
+    write: [{ filename: cachePath }],
+    status: 0
+  });
+
+  const cacheContents = res.write[0].content;
+
+  runPrettier(
+    "cli/only-changed",
+    ["--write", "--only-changed", "formatted.js"],
+    {
+      virtualFiles: {
+        [cachePath]: cacheContents
+      }
+    }
+  ).test({
+    write: [{ filename: cachePath, content: cacheContents }],
+    status: 0
+  });
+});
+
+describe("detect config change with --write --only-changed + unformatted file", () => {
+  const resBefore = runPrettier("cli/only-changed", [
+    "--write",
+    "--only-changed",
+    "unformatted.js"
+  ]).test({
+    write: [{ filename: "unformatted.js" }, { filename: cachePath }],
+    status: 0
+  });
+
+  const cacheContentsBefore = resBefore.write[1].content;
+
+  const resAfter = runPrettier(
+    "cli/only-changed",
+    ["--write", "--only-changed", "--use-tabs", "unformatted.js"],
+    {
+      virtualFiles: {
+        [cachePath]: cacheContentsBefore
+      }
+    }
+  ).test({
+    write: [{ filename: "unformatted.js" }, { filename: cachePath }],
+    status: 0
+  });
+
+  const cacheContentsAfter = resAfter.write[1].content;
+
+  expect(cacheContentsAfter).not.toBe(cacheContentsBefore);
+});
+
+describe("ChangedCache", () => {
+  it("should log errors when opening the cache file", () => {
+    const errLogger = jest.fn();
+    const msg = "open-cache-file-error";
+
+    new ChangedCache({
+      location: cachePath,
+      readFile: () => {
+        throw new Error(msg);
+      },
+      writeFile: () => {},
+      context: { logger: { error: errLogger } },
+      supportInfo: {}
+    });
+
+    expect(errLogger).toHaveBeenCalledWith(expect.stringContaining(msg));
+  });
+
+  it("should log errors when parsing the cache file", () => {
+    const errLogger = jest.fn();
+
+    new ChangedCache({
+      location: cachePath,
+      readFile: () => "invalid json",
+      writeFile: () => {},
+      context: { logger: { error: errLogger } },
+      supportInfo: {}
+    });
+
+    expect(errLogger).toHaveBeenCalledWith(
+      expect.stringContaining("cache content")
+    );
+  });
+
+  it("should log errors when closing the cache file", () => {
+    const errLogger = jest.fn();
+    const msg = "close-cache-file-error";
+
+    const changedCache = new ChangedCache({
+      location: cachePath,
+      readFile: () => "{}",
+      writeFile: () => {
+        throw new Error(msg);
+      },
+      context: { logger: { error: errLogger } },
+      supportInfo: {}
+    });
+    changedCache.close();
+
+    expect(errLogger).toHaveBeenCalledWith(expect.stringContaining(msg));
+  });
+
+  it("should log errors when serializing the cache contents", () => {
+    const errLogger = jest.fn();
+
+    const changedCache = new ChangedCache({
+      location: cachePath,
+      readFile: () => "{}",
+      writeFile: () => {},
+      context: { logger: { error: errLogger } },
+      supportInfo: {}
+    });
+    const mirror = {};
+    mirror.self = mirror;
+    changedCache.cache = mirror;
+    changedCache.close();
+
+    expect(errLogger).toHaveBeenCalledWith(
+      expect.stringContaining("serialize cache")
+    );
+  });
+});
diff --git a/tests_integration/cli/only-changed/formatted.js b/tests_integration/cli/only-changed/formatted.js
new file mode 100644
index 000000000..b506100a9
--- /dev/null
+++ b/tests_integration/cli/only-changed/formatted.js
@@ -0,0 +1 @@
+var x = 1;
diff --git a/tests_integration/cli/only-changed/unformatted.js b/tests_integration/cli/only-changed/unformatted.js
new file mode 100644
index 000000000..646611c06
--- /dev/null
+++ b/tests_integration/cli/only-changed/unformatted.js
@@ -0,0 +1 @@
+var x      =      1;
\ No newline at end of file
diff --git a/tests_integration/runPrettier.js b/tests_integration/runPrettier.js
index 27226065a..c1d62bc1e 100644
--- a/tests_integration/runPrettier.js
+++ b/tests_integration/runPrettier.js
@@ -64,6 +64,18 @@ function runPrettier(dir, args, options) {
     return origStatSync(filename);
   });
 
+  // Mock contents of "virtualFiles" when option is defined.
+  const origReadFileSync = fs.readFileSync;
+  jest.spyOn(fs, "readFileSync").mockImplementation((filename, opts) => {
+    if (
+      typeof options.virtualFiles === "object" &&
+      typeof options.virtualFiles[filename] === "string"
+    ) {
+      return options.virtualFiles[filename];
+    }
+    return origReadFileSync(filename, opts);
+  });
+
   const originalCwd = process.cwd();
   const originalArgv = process.argv;
   const originalExitCode = process.exitCode;
@@ -99,6 +111,11 @@ function runPrettier(dir, args, options) {
   jest
     .spyOn(require(thirdParty), "findParentDir")
     .mockImplementation(() => process.cwd());
+  jest
+    .spyOn(require(thirdParty), "writeFileAtomic")
+    .mockImplementation((filename, content) => {
+      write.push({ filename, content });
+    });
 
   try {
     require(prettierCli);
@@ -135,6 +152,9 @@ function runPrettier(dir, args, options) {
         if (name in testOptions) {
           if (name === "status" && testOptions[name] === "non-zero") {
             expect(value).not.toEqual(0);
+          } else if (name === "write") {
+            // Allows assertions on a subset of the "write" result. (ex. only file name)
+            expect(value).toMatchObject(testOptions[name]);
           } else {
             expect(value).toEqual(testOptions[name]);
           }
diff --git a/yarn.lock b/yarn.lock
index 3f811d0b2..e1d0c7913 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2691,6 +2691,15 @@ fill-range@^4.0.0:
     repeat-string "^1.6.1"
     to-regex-range "^2.1.0"
 
+find-cache-dir@1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/find-cache-dir/-/find-cache-dir-1.0.0.tgz#9288e3e9e3cc3748717d39eade17cf71fc30ee6f"
+  integrity sha1-kojj6ePMN0hxfTnq3hfPcfww7m8=
+  dependencies:
+    commondir "^1.0.1"
+    make-dir "^1.0.0"
+    pkg-dir "^2.0.0"
+
 find-cache-dir@^2.0.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/find-cache-dir/-/find-cache-dir-2.1.0.tgz#8d0f94cd13fe43c6c7c261a0d86115ca918c05f7"
@@ -6747,9 +6756,10 @@ wrappy@1:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
 
-write-file-atomic@^2.1.0:
+write-file-atomic@2.3.0, write-file-atomic@^2.1.0:
   version "2.3.0"
   resolved "https://registry.yarnpkg.com/write-file-atomic/-/write-file-atomic-2.3.0.tgz#1ff61575c2e2a4e8e510d6fa4e243cce183999ab"
+  integrity sha512-xuPeK4OdjWqtfi59ylvVL0Yn35SF3zgcAcv7rBPFHVaEapaDr4GdGgm3j7ckTwH9wHL7fGmgfAnb0+THrHb8tA==
   dependencies:
     graceful-fs "^4.1.11"
     imurmurhash "^0.1.4"