diff --git a/.gitignore b/.gitignore
index 8ad66d40..9d3ff0d7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,5 @@
 /.idea/
+/lib-es5/
 /node_modules/
 /*.log
+/.DS_Store
diff --git a/README.md b/README.md
index dd69daf4..add50133 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@ Options
   -g, --global          Look at global modules.
   -s, --skip-unused     Skip check for unused packages.
   -p, --production      Skip devDependencies.
-  -d, --dev-only        Look at devDependencies only (skip dependencies).
+  -d, --dev-only        Look at devDependencies only (skip dependencies and peerDependencies).
   -i, --ignore          Ignore dependencies based on succeeding glob.
   -E, --save-exact      Save exact version (x.y.z) instead of caret (^x.y.z) in package.json.
   --no-color            Force or disable color output.
@@ -120,13 +120,13 @@ This is enabled by default when using `global` or `update`.
 
 #### `-p, --production`
 
-By default `npm-check` will look at packages listed as `dependencies` and `devDependencies`.
+By default `npm-check` will look at packages listed as `dependencies`, `peerDependencies` and `devDependencies`.
 
 This option will let it ignore outdated and unused checks for packages listed as `devDependencies`.
 
 #### `-d, --dev-only`
 
-Ignore `dependencies` and only check `devDependencies`.
+Ignore `dependencies` and `peerDependencies` and only check `devDependencies`.
 
 This option will let it ignore outdated and unused checks for packages listed as `dependencies`.
 
@@ -140,7 +140,7 @@ Ignore dependencies that match specified glob.
 
 Install packages using `--save-exact`, meaning exact versions will be saved in package.json.
 
-Applies to both `dependencies` and `devDependencies`.
+Applies to `dependencies`, `peerDependencies` and `devDependencies`.
 
 #### `--color, --no-color`
 
@@ -194,7 +194,7 @@ npmCheck(options)
 
 ### `devOnly`
 
-* Ignore `dependencies` and only check `devDependencies`.
+* Ignore `dependencies` and `peerDependencies` and only check `devDependencies`.
 * default is `false`
 
 #### `cwd`
diff --git a/lib/in/create-package-summary.js b/lib/in/create-package-summary.js
index 37266df4..8e12c55c 100644
--- a/lib/in/create-package-summary.js
+++ b/lib/in/create-package-summary.js
@@ -24,6 +24,7 @@ function createPackageSummary(moduleName, currentState) {
 
     // Ignore packages that are using github or file urls
     const packageJsonVersion = cwdPackageJson.dependencies[moduleName] ||
+        cwdPackageJson.peerDependencies[moduleName] ||
         cwdPackageJson.devDependencies[moduleName] ||
         currentState.get('globalPackages')[moduleName];
 
diff --git a/lib/in/get-unused-packages.js b/lib/in/get-unused-packages.js
index 745c8fd7..e84e456d 100644
--- a/lib/in/get-unused-packages.js
+++ b/lib/in/get-unused-packages.js
@@ -49,14 +49,16 @@ function checkUnused(currentState) {
         depcheck(currentState.get('cwd'), depCheckOptions, resolve);
     }).then(depCheckResults => {
         spinner.stop();
-        const unusedDependencies = [].concat(depCheckResults.dependencies, depCheckResults.devDependencies);
+        const unusedDependencies =
+          [].concat(depCheckResults.dependencies, depCheckResults.peerDependencies, depCheckResults.devDependencies);
         currentState.set('unusedDependencies', unusedDependencies);
 
         const cwdPackageJson = currentState.get('cwdPackageJson');
 
         // currently missing will return devDependencies that aren't really missing
         const missingFromPackageJson = _.omit(depCheckResults.missing || {},
-                    Object.keys(cwdPackageJson.dependencies), Object.keys(cwdPackageJson.devDependencies));
+                    Object.keys(cwdPackageJson.dependencies), Object.keys(cwdPackageJson.peerDependencies),
+                    Object.keys(cwdPackageJson.devDependencies));
         currentState.set('missingFromPackageJson', missingFromPackageJson);
         return currentState;
     });
diff --git a/lib/in/index.js b/lib/in/index.js
index 1193ae1b..07078701 100644
--- a/lib/in/index.js
+++ b/lib/in/index.js
@@ -21,14 +21,14 @@ module.exports = function (currentState) {
             }
 
             if (currentState.get('ignoreDev')) {
-                return pkg.dependencies;
+                return merge(pkg.dependencies, pkg.peerDependencies);
             }
 
             if (currentState.get('devOnly')) {
                 return pkg.devDependencies;
             }
 
-            return merge(pkg.dependencies, pkg.devDependencies);
+            return merge(pkg.dependencies, pkg.peerDependencies, pkg.devDependencies);
         }
 
         const allDependencies = dependencies(cwdPackageJson);
diff --git a/lib/in/read-package-json.js b/lib/in/read-package-json.js
index b61df5b6..b28507ad 100644
--- a/lib/in/read-package-json.js
+++ b/lib/in/read-package-json.js
@@ -14,7 +14,7 @@ function readPackageJson(filename) {
             error = new Error(`A package.json was found at ${filename}, but it is not valid.`);
         }
     }
-    return merge(pkg, {devDependencies: {}, dependencies: {}, error: error});
+    return merge(pkg, {devDependencies: {}, peerDependencies: {}, dependencies: {}, error: error});
 }
 
 module.exports = readPackageJson;
diff --git a/lib/state/state.js b/lib/state/state.js
index 9213cb47..ebc252b0 100644
--- a/lib/state/state.js
+++ b/lib/state/state.js
@@ -21,7 +21,7 @@ const defaultOptions = {
     ignore: [],
 
     globalPackages: {},
-    cwdPackageJson: {devDependencies: {}, dependencies: {}},
+    cwdPackageJson: {devDependencies: {}, dependencies: {}, peerDependencies: {}},
 
     packages: false,
     unusedDependencies: false,
diff --git a/package.json b/package.json
index bd37ad32..b95f6edf 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "npm-check",
-  "version": "5.4.0",
+  "version": "5.5.0",
   "description": "Check for outdated, incorrect, and unused dependencies.",
   "main": "lib",
   "engines": {
@@ -50,7 +50,8 @@
     "updating",
     "updater",
     "installer",
-    "devDependencies"
+    "devDependencies",
+    "peerDependencies"
   ],
   "author": {
     "name": "Dylan Greene",
diff --git a/templates/readme/api.md b/templates/readme/api.md
index bad56cb7..060de20a 100644
--- a/templates/readme/api.md
+++ b/templates/readme/api.md
@@ -33,7 +33,7 @@ npmCheck(options)
 
 ### `devOnly`
 
-* Ignore `dependencies` and only check `devDependencies`.
+* Ignore `dependencies` and `peerDependencies` and only check `devDependencies`.
 * default is `false`
 
 ### `cwd`
diff --git a/templates/readme/cli.md b/templates/readme/cli.md
index 908b684b..b1239123 100644
--- a/templates/readme/cli.md
+++ b/templates/readme/cli.md
@@ -92,7 +92,7 @@ This is enabled by default when using `global` or `update`.
 
 ### `-p, --production`
 
-By default `npm-check` will look at packages listed as `dependencies` and `devDependencies`.
+By default `npm-check` will look at packages listed as `dependencies`, `peerDependencies` and `devDependencies`.
 
 This option will let it ignore outdated and unused checks for packages listed as `devDependencies`.
 
@@ -106,7 +106,7 @@ Ignore dependencies that match specified glob.
 
 Install packages using `--save-exact`, meaning exact versions will be saved in package.json.
 
-Applies to both `dependencies` and `devDependencies`.
+Applies to `dependencies`, `peerDependencies` and `devDependencies`.
 
 ### `--color, --no-color`