Backbone.js is a JavaScript library with a RESTful JSON interface and is based on the model–view–presenter(MVP) application design paradigm. Backbone is known for being lightweight, as its only dependency is on one JavaScript library UnderscoreJs. It is designed for developing single-page web applications and for keeping various parts of web applications (e.g. multiple clients and the server) synchronized.

Backbone was created by Jeremy Ashkenas, who is also known for CoffeeScript.