diff --git a/lib/functions/acos.js b/lib/functions/acos.js
new file mode 100644
index 000000000..f4479db97
--- /dev/null
+++ b/lib/functions/acos.js
@@ -0,0 +1,20 @@
+var utils = require('../utils')
+  , nodes = require('../nodes')
+	, convert = require('./convert-angle')
+	, asin    = require('./asin');
+
+/**
+ * Return the arccosine of the given `value`.
+ *
+ * @param {Double} trigValue
+ * @param {Unit} output 
+ * @return {Unit}
+ * @api public
+ */
+module.exports = function acos(trigValue, output) {
+	var output = typeof output !== 'undefined' ? output : 'deg';
+	var convertedValue = convert(Math.PI / 2, output) - asin(trigValue, output).val;
+	var m = Math.pow(10, 9);
+	convertedValue = Math.round(convertedValue * m) / m;
+  return new nodes.Unit(convertedValue, output);
+};
diff --git a/lib/functions/asin.js b/lib/functions/asin.js
new file mode 100644
index 000000000..5cfbcff78
--- /dev/null
+++ b/lib/functions/asin.js
@@ -0,0 +1,21 @@
+var utils = require('../utils')
+  , nodes = require('../nodes')
+	, convert = require('./convert-angle');
+
+/**
+ * Return the arcsine of the given `value`.
+ *
+ * @param {Double} trigValue
+ * @param {Unit} output 
+ * @return {Unit}
+ * @api public
+ */
+
+module.exports = function atan(trigValue, output) {
+	var output = typeof output !== 'undefined' ? output : 'deg';
+  var m = Math.pow(10, 9);
+	var value = Math.asin(trigValue) ;
+	var convertedValue = convert(value, output);
+	convertedValue = Math.round(convertedValue * m) / m;
+  return new nodes.Unit(convertedValue, output);
+};
diff --git a/lib/functions/atan.js b/lib/functions/atan.js
new file mode 100644
index 000000000..90501650d
--- /dev/null
+++ b/lib/functions/atan.js
@@ -0,0 +1,21 @@
+var utils = require('../utils')
+  , nodes = require('../nodes')
+	, convert = require('./convert-angle');
+
+/**
+ * Return the arctangent of the given `value`.
+ *
+ * @param {Double} trigValue
+ * @param {Unit} output 
+ * @return {Unit}
+ * @api public
+ */
+
+module.exports = function atan(trigValue, output) {
+	var output = typeof output !== 'undefined' ? output : 'deg';
+	var value = Math.atan(trigValue) ;
+	var m = Math.pow(10, 9);
+	var convertedValue = convert(value, output);
+	convertedValue = Math.round(convertedValue * m) / m;
+  return new nodes.Unit(convertedValue, output);
+};
diff --git a/lib/functions/convert-angle.js b/lib/functions/convert-angle.js
new file mode 100644
index 000000000..d0832f26e
--- /dev/null
+++ b/lib/functions/convert-angle.js
@@ -0,0 +1,19 @@
+
+/**
+ * Convert given value's base into the parameter unitName
+ *
+ * @param {Double} value
+ * @param {String} unitName
+ * @return {Double}
+ * @api private
+ */
+
+module.exports = function convertAngle(value, unitName) {
+	var factors = {
+		"rad" : 1,
+		"deg" : 180 / Math.PI,
+		"turn": 0.5 / Math.PI,
+		"grad": 200 / Math.PI
+	}
+	return value * factors[unitName];
+}
diff --git a/lib/functions/index.js b/lib/functions/index.js
index e292ed474..ec2a372a2 100644
--- a/lib/functions/index.js
+++ b/lib/functions/index.js
@@ -46,6 +46,9 @@ exports.red = require('./red');
 exports.remove = require('./remove');
 exports.replace = require('./replace');
 exports.rgb = require('./rgb');
+exports.atan = require('./atan');
+exports.asin = require('./asin');
+exports.acos = require('./acos');
 exports.rgba = require('./rgba');
 exports.s = require('./s');
 exports.saturation = require('./saturation');
diff --git a/test/cases/bifs.math.css b/test/cases/bifs.math.css
index 632a7a9fb..d56444912 100644
--- a/test/cases/bifs.math.css
+++ b/test/cases/bifs.math.css
@@ -67,3 +67,12 @@
   test8: -0.707106781;
   test9: -0.5;
 }
+.math_atan {
+  test1: 45deg;
+}
+.math_asin {
+  test1: 44.999999985deg;
+}
+.math_acos {
+  test1: 45.000000015deg;
+}
diff --git a/test/cases/bifs.math.styl b/test/cases/bifs.math.styl
index 0195ea877..aaba9310f 100644
--- a/test/cases/bifs.math.styl
+++ b/test/cases/bifs.math.styl
@@ -62,3 +62,12 @@
   test7: sin(5*PI/3)
   test8: sin(7*PI/4)
   test9: sin(11*PI/6)
+
+.math_atan
+  test1: atan(tan(45deg)) 
+
+.math_asin
+  test1: asin(sin(45deg)) 
+
+.math_acos
+  test1: acos(cos(45deg))