Backbone is a JavaScript library that helps us structure applications by implementing a version of the MV* pattern, which helps us separate different application concerns. The main Backbone components include models, collections, views, and routers; all these components communicate among themselves by triggering and listening to events.

The only hard dependency of Backbone is Underscore, which is a small utility library that provides functional programming support for collections, arrays, functions, and objects. It also provides additional utilities, such as a small template engine, which we will use later. To use the Backbone router and manipulate the DOM, jQuery or Zepto must also be included.