diff --git a/README.md b/README.md
index 937fdcdc..3d6d8531 100644
--- a/README.md
+++ b/README.md
@@ -274,6 +274,17 @@ you can pass `--no-config` instead.
 
 Path to a file containing patterns that describe files to ignore.  By default, prettier looks for `./.prettierignore`.
 
+#### `--require-pragma`
+
+Require a special comment, called a pragma, to be present in the file's first docblock comment in order for prettier to format it.
+```js
+/**
+ * @prettier
+ */
+```
+
+Valid pragmas are `@prettier` and `@format`.
+
 #### `--list-different`
 
 Another useful flag is `--list-different` (or `-l`) which prints the filenames of files that are different from Prettier formatting. If there are differences the script errors out, which is useful in a CI scenario.
@@ -288,7 +299,7 @@ Do not look for a configuration file.  The default settings will be used.
 
 #### `--config-precedence`
 
-Defines how config file should be evaluated in combination of CLI options. 
+Defines how config file should be evaluated in combination of CLI options.
 
 **cli-override (default)**
 
diff --git a/docs/options.md b/docs/options.md
index 06406013..67c339da 100644
--- a/docs/options.md
+++ b/docs/options.md
@@ -133,3 +133,26 @@ Default | CLI Override | API Override
 --------|--------------|-------------
 None | `--stdin-filepath <string>` | `filepath: "<string>"`
 
+## Require pragma
+Prettier can restrict itself to only format files that contain a special comment, called a pragma, at the top of the file. This is very useful
+when gradually transitioning large, unformatted codebases to prettier.
+
+For example, a file with the following as its first comment will be formatted when `--require-pragma` is supplied:
+
+```js
+/**
+ * @prettier
+ */
+```
+
+or
+
+```js
+/**
+ * @format
+ */
+```
+
+Default | CLI Override | API Override
+--------|--------------|-------------
+None | `--require-pragma` | `requirePragma`
diff --git a/index.js b/index.js
index cb351acc..25452ce7 100644
--- a/index.js
+++ b/index.js
@@ -10,6 +10,7 @@ const normalizeOptions = require("./src/options").normalize;
 const parser = require("./src/parser");
 const printDocToDebug = require("./src/doc-debug").printDocToDebug;
 const config = require("./src/resolve-config");
+const docblock = require("jest-docblock");
 
 function guessLineEnding(text) {
   const index = text.indexOf("\n");
@@ -30,6 +31,11 @@ function attachComments(text, ast, opts) {
   return astComments;
 }
 
+function hasPragma(text) {
+  const pragmas = Object.keys(docblock.parse(docblock.extract(text)));
+  return pragmas.indexOf("prettier") !== -1 || pragmas.indexOf("format") !== -1;
+}
+
 function ensureAllCommentsPrinted(astComments) {
   if (!astComments) {
     return;
@@ -56,6 +62,10 @@ function ensureAllCommentsPrinted(astComments) {
 }
 
 function formatWithCursor(text, opts, addAlignmentSize) {
+  if (opts.requirePragma && !hasPragma(text)) {
+    return { formatted: text };
+  }
+
   text = stripBom(text);
   addAlignmentSize = addAlignmentSize || 0;
 
diff --git a/package.json b/package.json
index 305b4f87..49db81f5 100644
--- a/package.json
+++ b/package.json
@@ -23,6 +23,7 @@
     "globby": "^6.1.0",
     "graphql": "0.10.1",
     "ignore": "^3.3.3",
+    "jest-docblock": "^21.0.2",
     "jest-validate": "20.0.3",
     "minimatch": "3.0.4",
     "minimist": "1.2.0",
diff --git a/src/cli-constant.js b/src/cli-constant.js
index 516475bd..05de15a9 100644
--- a/src/cli-constant.js
+++ b/src/cli-constant.js
@@ -7,7 +7,8 @@ const booleanOptionNames = [
   "bracket-spacing",
   "jsx-bracket-same-line",
   // Deprecated in 0.0.10
-  "flow-parser"
+  "flow-parser",
+  "require-pragma"
 ];
 
 const stringOptionNames = [
@@ -86,6 +87,8 @@ Available options:
                            Finds and prints the path to a configuration file for a given input file.
   --ignore-path <path>     Path to a file containing patterns that describe files to ignore.
                            Defaults to ./.prettierignore.
+  --require-pragma
+                           Require either '@prettier' or '@format' to be present in the file's first docblock comment in order for it to be formatted.
   --stdin                  Read input from stdin.
   --stdin-filepath         Path to the file used to read from stdin.
   --print-width <int>      Specify the length of line that the printer will wrap on. Defaults to 80.
diff --git a/src/cli-util.js b/src/cli-util.js
index 3fd50001..c6b6952e 100644
--- a/src/cli-util.js
+++ b/src/cli-util.js
@@ -25,6 +25,7 @@ function getOptions(argv) {
     printWidth: getIntOption(argv, "print-width"),
     tabWidth: getIntOption(argv, "tab-width"),
     bracketSpacing: argv["bracket-spacing"],
+    requirePragma: argv["require-pragma"],
     singleQuote: argv["single-quote"],
     jsxBracketSameLine: argv["jsx-bracket-same-line"],
     filepath: argv["stdin-filepath"],
diff --git a/src/options.js b/src/options.js
index 25ad8c86..fb824ae5 100644
--- a/src/options.js
+++ b/src/options.js
@@ -15,6 +15,7 @@ const defaults = {
   bracketSpacing: true,
   jsxBracketSameLine: false,
   parser: "babylon",
+  requirePragma: false,
   semi: true
 };
 
diff --git a/tests/require-pragma/__snapshots__/jsfmt.spec.js.snap b/tests/require-pragma/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 00000000..66392b09
--- /dev/null
+++ b/tests/require-pragma/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,59 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`module-with-pragma.js 1`] = `
+/**
+ * @flow
+ * @format
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ * @format
+ */
+
+function foo(bar) {
+  return bar + 3 + 4;
+}
+
+`;
+
+exports[`module-without-pragma.js 1`] = `
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
+
+`;
diff --git a/tests/require-pragma/jsfmt.spec.js b/tests/require-pragma/jsfmt.spec.js
new file mode 100644
index 00000000..61c7d29f
--- /dev/null
+++ b/tests/require-pragma/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname, { requirePragma: true });
diff --git a/tests/require-pragma/module-with-pragma.js b/tests/require-pragma/module-with-pragma.js
new file mode 100644
index 00000000..79499ba9
--- /dev/null
+++ b/tests/require-pragma/module-with-pragma.js
@@ -0,0 +1,14 @@
+/**
+ * @flow
+ * @format
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
diff --git a/tests/require-pragma/module-without-pragma.js b/tests/require-pragma/module-without-pragma.js
new file mode 100644
index 00000000..8ece3791
--- /dev/null
+++ b/tests/require-pragma/module-without-pragma.js
@@ -0,0 +1,13 @@
+/**
+ * @flow
+ */
+
+function      foo(bar)
+
+
+{
+
+  return bar +
+    3 +
+  4;
+}
diff --git a/tests_integration/__tests__/__snapshots__/early-exit.js.snap b/tests_integration/__tests__/__snapshots__/early-exit.js.snap
index 00097955..c41392de 100644
--- a/tests_integration/__tests__/__snapshots__/early-exit.js.snap
+++ b/tests_integration/__tests__/__snapshots__/early-exit.js.snap
@@ -19,6 +19,8 @@ Available options:
                            Finds and prints the path to a configuration file for a given input file.
   --ignore-path <path>     Path to a file containing patterns that describe files to ignore.
                            Defaults to ./.prettierignore.
+  --require-pragma
+                           Require either '@prettier' or '@format' to be present in the file's first docblock comment in order for it to be formatted.
   --stdin                  Read input from stdin.
   --stdin-filepath         Path to the file used to read from stdin.
   --print-width <int>      Specify the length of line that the printer will wrap on. Defaults to 80.
diff --git a/yarn.lock b/yarn.lock
index fbdccb6d..da7e212c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2258,6 +2258,10 @@ jest-docblock@^20.0.1, jest-docblock@^20.0.3:
   version "20.0.3"
   resolved "https://registry.yarnpkg.com/jest-docblock/-/jest-docblock-20.0.3.tgz#17bea984342cc33d83c50fbe1545ea0efaa44712"
 
+jest-docblock@^21.0.2:
+  version "21.0.2"
+  resolved "https://registry.yarnpkg.com/jest-docblock/-/jest-docblock-21.0.2.tgz#66f69ddb440799fc32f91d0ac3d8d35e99e2032f"
+
 jest-environment-jsdom@^20.0.3:
   version "20.0.3"
   resolved "https://registry.yarnpkg.com/jest-environment-jsdom/-/jest-environment-jsdom-20.0.3.tgz#048a8ac12ee225f7190417713834bb999787de99"