diff --git a/decimal.js b/decimal.js
index 511028e..e58df57 100644
--- a/decimal.js
+++ b/decimal.js
@@ -2629,9 +2629,9 @@
    */
   function cosine(Ctor, x) {
     var k, len, y;
-    
+
     if (x.isZero()) return x;
-    
+
     // Argument reduction: cos(4x) = 8*(cos^4(x) - cos^2(x)) + 1
     // i.e. cos(x) = 8*(cos^4(x/4) - cos^2(x/4)) + 1
 
@@ -3665,10 +3665,10 @@
   function sine(Ctor, x) {
     var k,
       len = x.d.length;
-    
+
     if (len < 3) {
       return x.isZero() ? x : taylorSeries(Ctor, 2, x, x);
-    }  
+    }
 
     // Argument reduction: sin(5x) = 16*sin^5(x) - 20*sin^3(x) + 5*sin(x)
     // i.e. sin(x) = 16*sin^5(x/5) - 20*sin^3(x/5) + 5*sin(x/5)
@@ -3959,6 +3959,7 @@
    *  sinh
    *  sqrt
    *  sub
+   *  sum
    *  tan
    *  tanh
    *  trunc
@@ -4407,6 +4408,7 @@
     Decimal.sinh = sinh;          // ES6
     Decimal.sqrt = sqrt;
     Decimal.sub = sub;
+    Decimal.sum = sum;
     Decimal.tan = tan;
     Decimal.tanh = tanh;          // ES6
     Decimal.trunc = trunc;        // ES6
@@ -4801,6 +4803,28 @@
   }
 
 
+  /*
+   * Return a new Decimal whose value is the sum of the arguments, rounded to `precision`
+   * significant digits using rounding mode `rounding`.
+   *
+   * Only the result is rounded, not the intermediate calculations.
+   *
+   * arguments {number|string|Decimal}
+   *
+   */
+  function sum() {
+    var i = 0,
+      args = arguments,
+      x = new this(args[i]);
+
+    external = false;
+    for (; x.s && ++i < args.length;) x = x.plus(args[i]);
+    external = true;
+
+    return finalise(x, this.precision, this.rounding);
+  }
+
+
   /*
    * Return a new Decimal whose value is the tangent of `x`, rounded to `precision` significant
    * digits using rounding mode `rounding`.
diff --git a/decimal.mjs b/decimal.mjs
index 81b7086..a319764 100644
--- a/decimal.mjs
+++ b/decimal.mjs
@@ -2624,13 +2624,15 @@ function convertBase(str, baseIn, baseOut) {
  *
  */
 function cosine(Ctor, x) {
-  var k, y,
-    len = x.d.length;
+  var k, len, y;
+  
+  if (x.isZero()) return x;
 
   // Argument reduction: cos(4x) = 8*(cos^4(x) - cos^2(x)) + 1
   // i.e. cos(x) = 8*(cos^4(x/4) - cos^2(x/4)) + 1
 
   // Estimate the optimum number of times to use the argument reduction.
+  len = x.d.length;
   if (len < 32) {
     k = Math.ceil(len / 3);
     y = (1 / tinyPow(4, k)).toString();
@@ -3660,7 +3662,9 @@ function sine(Ctor, x) {
   var k,
     len = x.d.length;
 
-  if (len < 3) return taylorSeries(Ctor, 2, x, x);
+  if (len < 3) {
+    return x.isZero() ? x : taylorSeries(Ctor, 2, x, x);
+  }                                                       
 
   // Argument reduction: sin(5x) = 16*sin^5(x) - 20*sin^3(x) + 5*sin(x)
   // i.e. sin(x) = 16*sin^5(x/5) - 20*sin^3(x/5) + 5*sin(x/5)
@@ -3951,6 +3955,7 @@ function truncate(arr, len) {
  *  sinh
  *  sqrt
  *  sub
+ *  sum     
  *  tan
  *  tanh
  *  trunc
@@ -4399,6 +4404,7 @@ function clone(obj) {
   Decimal.sinh = sinh;          // ES6
   Decimal.sqrt = sqrt;
   Decimal.sub = sub;
+  Decimal.sum = sum;                    
   Decimal.tan = tan;
   Decimal.tanh = tanh;          // ES6
   Decimal.trunc = trunc;        // ES6
@@ -4793,6 +4799,28 @@ function sub(x, y) {
 }
 
 
+/*
+ * Return a new Decimal whose value is the sum of the arguments, rounded to `precision`
+ * significant digits using rounding mode `rounding`.
+ *
+ * Only the result is rounded, not the intermediate calculations.
+ *
+ * arguments {number|string|Decimal}
+ *
+ */
+function sum() {
+  var i = 0,
+    args = arguments,
+    x = new this(args[i]);
+
+  external = false;
+  for (; x.s && ++i < args.length;) x = x.plus(args[i]);
+  external = true;
+
+  return finalise(x, this.precision, this.rounding);
+}
+
+
 /*
  * Return a new Decimal whose value is the tangent of `x`, rounded to `precision` significant
  * digits using rounding mode `rounding`.
diff --git a/doc/API.html b/doc/API.html
index 9eb8e14..7af7e90 100644
--- a/doc/API.html
+++ b/doc/API.html
@@ -102,6 +102,7 @@ li span{float:right;margin-right:10px;color:#c0c0c0}
       <li><a href="#Dsinh"      >sinh</a></li>
       <li><a href="#Dsqrt"      >sqrt</a></li>
       <li><a href="#Dsub"       >sub</a></li>
+      <li><a href="#Dsum"       >sum</a></li>
       <li><a href="#Dtan"       >tan</a></li>
       <li><a href="#Dtanh"      >tanh</a></li>
       <li><a href="#Dtrunc"     >trunc</a></li>
@@ -601,7 +602,7 @@ a.equals(b)                    // true</pre>
 
 
     <h5 id="Dmax">
-      max<code class='inset'>.max([x [, y, ...]]) <i>&rArr; Decimal</i></code>
+      max<code class='inset'>.max(x [, y, ...]) <i>&rArr; Decimal</i></code>
     </h5>
     <p>
       <code>x</code>: <i>number|string|Decimal</i><br />
@@ -613,7 +614,7 @@ a.equals(b)                    // true</pre>
 
 
     <h5 id="Dmin">
-      min<code class='inset'>.min([x [, y, ...]]) <i>&rArr; Decimal</i></code>
+      min<code class='inset'>.min(x [, y, ...]) <i>&rArr; Decimal</i></code>
     </h5>
     <p>
       <code>x</code>: <i>number|string|Decimal</i><br />
@@ -833,7 +834,7 @@ a.equals(b)                    // true</pre>
 
 
 
-      <h5 id="Dsub">sub<code class='inset'>.sub(x, y) <i>&rArr; Decimal</i></code></h5>
+    <h5 id="Dsub">sub<code class='inset'>.sub(x, y) <i>&rArr; Decimal</i></code></h5>
     <p>
       <code>x</code>: <i>number|string|Decimal</i><br />
       <code>y</code>: <i>number|string|Decimal</i>
@@ -845,7 +846,26 @@ a.equals(b)                    // true</pre>
 
 
 
-     <h5 id="Dtan">tan<code class='inset'>.tan(x) <i>&rArr; Decimal</i></code></h5>
+    <h5 id="Dsum">sum<code class='inset'>.sum(x [, y, ...]) <i>&rArr; Decimal</i></code></h5>
+    <p>
+      <code>x</code>: <i>number|string|Decimal</i><br />
+      <code>y</code>: <i>number|string|Decimal</i>
+    </p>
+    <p>
+      Returns a new Decimal whose value is the sum of the <code>arguments</code>,
+      rounded to <a href='#precision'><code>precision</code></a> significant digits using
+      rounding mode <a href='#rounding'><code>rounding</code></a>.<br />
+      Only the result is rounded, not the intermediate summations.
+    </p>
+    <pre>
+x = 5
+y = '16'
+z = new Decimal(-11)
+Decimal.sum(x, y, z)           // '10'</pre>
+
+
+
+    <h5 id="Dtan">tan<code class='inset'>.tan(x) <i>&rArr; Decimal</i></code></h5>
     <p><code>x</code>: <i>number|string|Decimal</i></p>
     <p>See <code><a href='#tan'>tangent</a></code>.</p>
     <pre>a = Decimal.tan(x)
diff --git a/test/modules/sum.js b/test/modules/sum.js
new file mode 100644
index 0000000..6dda6f0
--- /dev/null
+++ b/test/modules/sum.js
@@ -0,0 +1,64 @@
+if (typeof T === 'undefined') require('../setup');
+
+T('sum', function () {
+  var expected;
+
+  function t() {
+    T.assertEqualDecimal(expected, Decimal.sum.apply(Decimal, arguments));
+  }
+
+  expected = new Decimal(0);
+
+  t('0');
+  t('0', new Decimal(0));
+  t(1, 0, '-1');
+  t(0, new Decimal('-10'), 0, 0, 0, 0, 0, 10);
+  t(11, -11);
+  t(1, '2', new Decimal(3), new Decimal('4'), -10);
+  t(new Decimal(-10), '9', new Decimal(0.01), 0.99);
+  
+  expected = new Decimal(10);
+
+  t('10');
+  t('0', new Decimal('10'));
+  t(10, 0);
+  t(0, 0, 0, 0, 0, 0, 10);
+  t(11, -1);
+  t(1, '2', new Decimal(3), new Decimal('4'));
+  t('9', new Decimal(0.01), 0.99);
+
+  expected = new Decimal(600);
+
+  t(100, 200, 300);
+  t('100', '200', '300');
+  t(new Decimal(100), new Decimal(200), new Decimal(300));
+  t(100, '200', new Decimal(300));
+  t(99.9, 200.05, 300.05);
+
+  expected = new Decimal(NaN);
+
+  t(NaN);
+  t('1', NaN);
+  t(100, 200, NaN);
+  t(NaN, 0, '9', new Decimal(0), 11, Infinity);
+  t(0, new Decimal('-Infinity'), '9', new Decimal(NaN), 11);
+  t(4, '-Infinity', 0, '9', new Decimal(0), Infinity, 2);
+
+  expected = new Decimal(Infinity);
+
+  t(Infinity);
+  t(1, '1e10000000000000000000000000000000000000000', '4');
+  t(100, 200, 'Infinity');
+  t(0, new Decimal('Infinity'), '9', new Decimal(0), 11);
+  t(0, '9', new Decimal(0), 11, Infinity);
+  t(4, new Decimal(Infinity), 0, '9', new Decimal(0), Infinity, 2);
+
+  expected = new Decimal(-Infinity);
+
+  t(-Infinity);
+  t(1, '-1e10000000000000000000000000000000000000000', '4');
+  t(100, 200, '-Infinity');
+  t(0, new Decimal('-Infinity'), '9', new Decimal(0), 11);
+  t(0, '9', new Decimal(0), 11, -Infinity);
+  t(4, new Decimal(-Infinity), 0, '9', new Decimal(0), -Infinity, 2);
+});
\ No newline at end of file
diff --git a/test/test.html b/test/test.html
index fd07521..7412f16 100644
--- a/test/test.html
+++ b/test/test.html
@@ -59,6 +59,7 @@
     'sin',
     'sinh',
     'sqrt',
+    'sum',
     'tan',
     'tanh',
     'times',
diff --git a/test/test.js b/test/test.js
index cdf4aca..bcc42f4 100644
--- a/test/test.js
+++ b/test/test.js
@@ -46,6 +46,7 @@ console.log('\n Testing decimal.js\n');
   'sin',
   'sinh',
   'sqrt',
+  'sum',
   'tan',
   'tanh',
   'times',