diff --git a/.jshintrc b/.jshintrc
index b199491a..1d2b6d52 100644
--- a/.jshintrc
+++ b/.jshintrc
@@ -6,7 +6,7 @@
         "it": false
     },
     "node": true,
-    "strict": false,
+    "globalstrict": true,
     "expr": true,
     "curly": false,
     "camelcase": true,
diff --git a/examples/fromFile.js b/examples/fromFile.js
index c9595eb1..1565afe1 100644
--- a/examples/fromFile.js
+++ b/examples/fromFile.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var SVGO = require('../lib/svgo'),
     svgo = new SVGO(/*{ custom config object }*/);
 
diff --git a/examples/fromStream.js b/examples/fromStream.js
index 13d88508..4840163e 100644
--- a/examples/fromStream.js
+++ b/examples/fromStream.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var FS = require('fs'),
     PATH = require('path'),
     path = PATH.resolve(__dirname, '../examples/test.svg'),
diff --git a/examples/fromString.js b/examples/fromString.js
index 4a8f45cc..1c371090 100644
--- a/examples/fromString.js
+++ b/examples/fromString.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var SVGO = require('../lib/svgo'),
     svgo = new SVGO(/*{ custom config object }*/);
 
diff --git a/lib/svgo.js b/lib/svgo.js
index ec7e8e53..8a9db98b 100644
--- a/lib/svgo.js
+++ b/lib/svgo.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * SVGO is a Nodejs-based tool for optimizing SVG vector graphics files.
  *
diff --git a/lib/svgo/coa.js b/lib/svgo/coa.js
index 4cd730ea..6cc5a677 100644
--- a/lib/svgo/coa.js
+++ b/lib/svgo/coa.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var FS = require('fs'),
     QFS = require('q-fs'),
     PATH = require('path'),
diff --git a/lib/svgo/config.js b/lib/svgo/config.js
index 426b3df4..b5e85421 100644
--- a/lib/svgo/config.js
+++ b/lib/svgo/config.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var QFS = require('q-fs'),
     PATH = require('path'),
     YAML = require('yamljs'),
diff --git a/lib/svgo/js2svg.js b/lib/svgo/js2svg.js
index f161cace..c10371e3 100644
--- a/lib/svgo/js2svg.js
+++ b/lib/svgo/js2svg.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var INHERIT = require('inherit'),
     extend = require('./tools').extend;
 
diff --git a/lib/svgo/jsAPI.js b/lib/svgo/jsAPI.js
index 0f0046ef..ac18de31 100644
--- a/lib/svgo/jsAPI.js
+++ b/lib/svgo/jsAPI.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var INHERIT = require('inherit'),
     extend = require('./tools').extend;
 
diff --git a/lib/svgo/plugins.js b/lib/svgo/plugins.js
index 2a937410..7098e766 100644
--- a/lib/svgo/plugins.js
+++ b/lib/svgo/plugins.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Plugins engine.
  *
diff --git a/lib/svgo/svg2js.js b/lib/svgo/svg2js.js
index 9367ea18..14c66ec8 100644
--- a/lib/svgo/svg2js.js
+++ b/lib/svgo/svg2js.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var Q = require('q'),
     SAX = require('sax'),
     JSAPI = require('./jsAPI');
diff --git a/lib/svgo/tools.js b/lib/svgo/tools.js
index 4242084c..76fe5240 100644
--- a/lib/svgo/tools.js
+++ b/lib/svgo/tools.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var datauriSVGPrefix = exports.datauriSVGPrefix = 'data:image/svg+xml;base64,';
 
 /**
diff --git a/plugins/_collections.js b/plugins/_collections.js
index f0f5ab20..5911cdf5 100644
--- a/plugins/_collections.js
+++ b/plugins/_collections.js
@@ -1,3 +1,5 @@
+'use strict';
+
 // http://www.w3.org/TR/SVG/intro.html#Definitions
 var elemsGroups = exports.elemsGroups = {
     animation: ['animate', 'animateColor', 'animateMotion', 'animateTransform', 'set'],
diff --git a/plugins/cleanupAttrs.js b/plugins/cleanupAttrs.js
index 096c1d83..09d34ae1 100644
--- a/plugins/cleanupAttrs.js
+++ b/plugins/cleanupAttrs.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var regNewlines = /\n/g,
     regSpaces = /\s{2,}/g;
 
diff --git a/plugins/cleanupEnableBackground.js b/plugins/cleanupEnableBackground.js
index b206ffa1..07c0519a 100644
--- a/plugins/cleanupEnableBackground.js
+++ b/plugins/cleanupEnableBackground.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var regEnableBackground = /^new\s0\s0\s(\d+)\s(\d+)$/,
     elems = ['svg', 'mask', 'pattern'];
 
diff --git a/plugins/cleanupSVGElem.js b/plugins/cleanupSVGElem.js
index ff51b1c3..677f3b3a 100644
--- a/plugins/cleanupSVGElem.js
+++ b/plugins/cleanupSVGElem.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove some useless svg element attributes.
  *
diff --git a/plugins/collapseGroups.js b/plugins/collapseGroups.js
index 429c93de..a32a2d83 100644
--- a/plugins/collapseGroups.js
+++ b/plugins/collapseGroups.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var flattenOneLevel = require('../lib/svgo/tools').flattenOneLevel;
 
 /*
diff --git a/plugins/convertColors.js b/plugins/convertColors.js
index 955a1dfb..bba7f4ee 100644
--- a/plugins/convertColors.js
+++ b/plugins/convertColors.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var collections = require('./_collections'),
     regRGB = /^rgb\((\d+%?),\s*(\d+%?),\s*(\d+%?)\)$/,
     regHEX = /^\#(([a-fA-F0-9])\2){3}$/;
diff --git a/plugins/convertPathData.js b/plugins/convertPathData.js
index 861115c1..a08530c8 100644
--- a/plugins/convertPathData.js
+++ b/plugins/convertPathData.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var cleanupOutData = require('../lib/svgo/tools').cleanupOutData,
     regPathInstructions = /([MmLlHhVvCcSsQqTtAaZz])\s*/,
     regPathData = /(?=-)|[\s,]+/,
diff --git a/plugins/convertStyleToAttrs.js b/plugins/convertStyleToAttrs.js
index 4cb8fcef..d634bbdd 100644
--- a/plugins/convertStyleToAttrs.js
+++ b/plugins/convertStyleToAttrs.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var extend = require('../lib/svgo/tools').extend,
     stylingProps = require('./_collections').stylingProps,
     regCleanupStyle = /(:|;)\s+/g;
diff --git a/plugins/convertTransform.js b/plugins/convertTransform.js
index c9773f1c..5530dc8b 100644
--- a/plugins/convertTransform.js
+++ b/plugins/convertTransform.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var cleanupOutData = require('../lib/svgo/tools').cleanupOutData,
     regTransformTypes = /matrix|translate|scale|rotate|skewX|skewY/,
     regTransformSplit = /(matrix|translate|scale|rotate|skewX|skewY)\s*\((.+?)\)[\s,]*/,
diff --git a/plugins/moveElemsAttrsToGroup.js b/plugins/moveElemsAttrsToGroup.js
index e521f43b..9fda50c4 100644
--- a/plugins/moveElemsAttrsToGroup.js
+++ b/plugins/moveElemsAttrsToGroup.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var inheritableAttrs = require('./_collections').inheritableAttrs;
 
 /**
diff --git a/plugins/removeComments.js b/plugins/removeComments.js
index 86912ab5..5bc2699f 100644
--- a/plugins/removeComments.js
+++ b/plugins/removeComments.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove comments.
  *
diff --git a/plugins/removeDefaultPx.js b/plugins/removeDefaultPx.js
index 76484b08..489172a2 100644
--- a/plugins/removeDefaultPx.js
+++ b/plugins/removeDefaultPx.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var regValPx = /^(-?(?:[0-9]+|[0-9]*\.[0-9]+))px$/;
 
 /**
diff --git a/plugins/removeDoctype.js b/plugins/removeDoctype.js
index c26e4feb..a3c21816 100644
--- a/plugins/removeDoctype.js
+++ b/plugins/removeDoctype.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove DOCTYPE declaration.
  *
diff --git a/plugins/removeEditorsNSData.js b/plugins/removeEditorsNSData.js
index 3c0e3db7..7e2ad4cd 100644
--- a/plugins/removeEditorsNSData.js
+++ b/plugins/removeEditorsNSData.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var editorNamespaces = require('./_collections').editorNamespaces,
     prefixes = [];
 
diff --git a/plugins/removeEmptyAttrs.js b/plugins/removeEmptyAttrs.js
index 56d18c57..519762fd 100644
--- a/plugins/removeEmptyAttrs.js
+++ b/plugins/removeEmptyAttrs.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove attributes with empty values.
  *
diff --git a/plugins/removeEmptyContainers.js b/plugins/removeEmptyContainers.js
index af86b644..ddf1c791 100644
--- a/plugins/removeEmptyContainers.js
+++ b/plugins/removeEmptyContainers.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var container = require('./_collections').elemsGroups.container;
 
 /**
diff --git a/plugins/removeEmptyText.js b/plugins/removeEmptyText.js
index a05de73b..9439332e 100644
--- a/plugins/removeEmptyText.js
+++ b/plugins/removeEmptyText.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove empty Text elements.
  *
diff --git a/plugins/removeHiddenElems.js b/plugins/removeHiddenElems.js
index 4ce0acb9..1ba4d730 100644
--- a/plugins/removeHiddenElems.js
+++ b/plugins/removeHiddenElems.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove hidden elements with disabled rendering:
  * - display="none"
diff --git a/plugins/removeMetadata.js b/plugins/removeMetadata.js
index 18365e9b..28f3d04b 100644
--- a/plugins/removeMetadata.js
+++ b/plugins/removeMetadata.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove <metadata>.
  *
diff --git a/plugins/removeUnknownsAndDefaults.js b/plugins/removeUnknownsAndDefaults.js
index 9d45c40b..b0998b09 100644
--- a/plugins/removeUnknownsAndDefaults.js
+++ b/plugins/removeUnknownsAndDefaults.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var flattenOneLevel = require('../lib/svgo/tools').flattenOneLevel,
     elems = require('./_collections').elems;
 
diff --git a/plugins/removeUnusedNS.js b/plugins/removeUnusedNS.js
index 075a2d74..72306d3a 100644
--- a/plugins/removeUnusedNS.js
+++ b/plugins/removeUnusedNS.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove unused namespaces declaration.
  *
diff --git a/plugins/removeViewBox.js b/plugins/removeViewBox.js
index d6cae64c..99a3c285 100644
--- a/plugins/removeViewBox.js
+++ b/plugins/removeViewBox.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var regViewBox = /^0\s0\s(\d+)\s(\d+)$/,
     viewBoxElems = ['svg', 'pattern'];
 
diff --git a/plugins/removeXMLProcInst.js b/plugins/removeXMLProcInst.js
index ad0d8a8f..83b867ae 100644
--- a/plugins/removeXMLProcInst.js
+++ b/plugins/removeXMLProcInst.js
@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Remove XML Processing Instruction.
  *
diff --git a/test/config/_index.js b/test/config/_index.js
index a93b5a7c..cc2f857d 100644
--- a/test/config/_index.js
+++ b/test/config/_index.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var cover = process.argv[3] === 'mocha-istanbul',
     config = require(cover ? '../../lib-cov/svgo/config' : '../../lib/svgo/config');
 
diff --git a/test/plugins/_index.js b/test/plugins/_index.js
index 6d09fc7c..c9366e4e 100644
--- a/test/plugins/_index.js
+++ b/test/plugins/_index.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var INHERIT = require('inherit'),
     QFS = require('q-fs'),
     FS = require('fs'),
diff --git a/test/svg2js/_index.js b/test/svg2js/_index.js
index 0154ac2e..a6771b37 100644
--- a/test/svg2js/_index.js
+++ b/test/svg2js/_index.js
@@ -1,3 +1,5 @@
+'use strict';
+
 var cover = process.argv[3] === 'mocha-istanbul',
     svg2js = require(cover ? '../../lib-cov/svgo/svg2js' : '../../lib/svgo/svg2js');