diff --git a/.gitignore b/.gitignore
index a22e55e..2b9d76a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,4 @@ components/
 coverage/
 node_modules/
 build.js
+.idea
diff --git a/index.js b/index.js
index f3912ee..8936d41 100644
--- a/index.js
+++ b/index.js
@@ -15,13 +15,16 @@
  *
  * @param {NLCSTNode|Array.<NLCSTNode>} node - Node to to
  *   stringify.
+ * @param {string} separator - a specified separator
  * @return {string} - Stringified `node`.
  */
-function nlcstToString(node) {
+function nlcstToString(node, separator) {
     var values;
     var length;
     var children;
 
+    separator = separator || '';
+
     if (typeof node.value === 'string') {
         return node.value;
     }
@@ -40,10 +43,10 @@ function nlcstToString(node) {
     values = [];
 
     while (length--) {
-        values[length] = nlcstToString(children[length]);
+        values[length] = nlcstToString(children[length], separator);
     }
 
-    return values.join('');
+    return values.join(separator);
 }
 
 /*
diff --git a/nlcst-to-string.js b/nlcst-to-string.js
index 94ea398..7d21825 100644
--- a/nlcst-to-string.js
+++ b/nlcst-to-string.js
@@ -16,13 +16,16 @@
  *
  * @param {NLCSTNode|Array.<NLCSTNode>} node - Node to to
  *   stringify.
+ * @param {string} separator - a specified separator
  * @return {string} - Stringified `node`.
  */
-function nlcstToString(node) {
+function nlcstToString(node, separator) {
     var values;
     var length;
     var children;
 
+    separator = separator || '';
+
     if (typeof node.value === 'string') {
         return node.value;
     }
@@ -41,10 +44,10 @@ function nlcstToString(node) {
     values = [];
 
     while (length--) {
-        values[length] = nlcstToString(children[length]);
+        values[length] = nlcstToString(children[length], separator);
     }
 
-    return values.join('');
+    return values.join(separator);
 }
 
 /*
diff --git a/nlcst-to-string.min.js b/nlcst-to-string.min.js
index d51ead6..71ed205 100644
--- a/nlcst-to-string.min.js
+++ b/nlcst-to-string.min.js
@@ -1 +1 @@
-!function(b,a){typeof exports==='object'&&typeof module!=='undefined'?module.exports=b():typeof define==='function'&&define.amd?define([],b):(typeof window!=='undefined'?a=window:typeof global!=='undefined'?a=global:typeof self!=='undefined'?a=self:a=this,a.nlcstToString=b())}(function(){return function a(b,c,e){function f(d,k){if(!c[d]){if(!b[d]){var i=typeof require=='function'&&require;if(!k&&i)return i(d,!0);if(g)return g(d,!0);var j=new Error("Cannot find module '"+d+"'");throw j.code='MODULE_NOT_FOUND',j}var h=c[d]={exports:{}};b[d][0].call(h.exports,function(c){var a=b[d][1][c];return f(a?a:c)},h,h.exports,a,b,c,e)}return c[d].exports}var g=typeof require=='function'&&require;for(var d=0;d<e.length;d++)f(e[d]);return f}({1:[function(c,b,d){'use strict';function a(b){var e,c,d;if(typeof b.value==='string')return b.value;if(d='length'in b?b:b.children,c=d.length,c===1&&'value'in d[0])return d[0].value;e=[];while(c--)e[c]=a(d[c]);return e.join('')}b.exports=a},{}]},{},[1])(1)})
+!function(b,a){typeof exports==='object'&&typeof module!=='undefined'?module.exports=b():typeof define==='function'&&define.amd?define([],b):(typeof window!=='undefined'?a=window:typeof global!=='undefined'?a=global:typeof self!=='undefined'?a=self:a=this,a.nlcstToString=b())}(function(){return function a(b,c,e){function f(d,k){if(!c[d]){if(!b[d]){var i=typeof require=='function'&&require;if(!k&&i)return i(d,!0);if(g)return g(d,!0);var j=new Error("Cannot find module '"+d+"'");throw j.code='MODULE_NOT_FOUND',j}var h=c[d]={exports:{}};b[d][0].call(h.exports,function(c){var a=b[d][1][c];return f(a?a:c)},h,h.exports,a,b,c,e)}return c[d].exports}var g=typeof require=='function'&&require;for(var d=0;d<e.length;d++)f(e[d]);return f}({1:[function(c,b,d){'use strict';function a(b,e){var f,c,d;if(e=e||'',typeof b.value==='string')return b.value;if(d='length'in b?b:b.children,c=d.length,c===1&&'value'in d[0])return d[0].value;f=[];while(c--)f[c]=a(d[c],e);return f.join(e)}b.exports=a},{}]},{},[1])(1)})
diff --git a/package.json b/package.json
index 353f78e..b77de64 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "nlcst-to-string",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "description": "Transform an NLCST node into a string",
   "license": "MIT",
   "keywords": [
diff --git a/test.js b/test.js
index 1bdafd4..d63f6e1 100644
--- a/test.js
+++ b/test.js
@@ -104,4 +104,37 @@ describe('toString()', function () {
             }
         ]), 'AT&T');
     });
+
+    it('should concatenate `children` with a separator', function () {
+        equal(toString({
+            'children': [
+                {
+                    'children': [
+                        {
+                            'value': 'AT'
+                        },
+                        {
+                            'value': '&'
+                        },
+                        {
+                            'value': 'T'
+                        }
+                    ]
+                },
+                {
+                    'children': [
+                        {
+                            'value': 'AT'
+                        },
+                        {
+                            'value': '&'
+                        },
+                        {
+                            'value': 'T'
+                        }
+                    ]
+                }
+            ]
+        }, ' '), 'AT & T AT & T');
+    });
 });