Single page applications (SPAs) are web applications that load all necessary content at once so that subsequent page changes do not require additional page loads, providing a more fluid user experience similar to a desktop application. SPAs use a combination of HTML, CSS, and JavaScript and are commonly built using frameworks like AngularJS, Ember.js, and Durandal. This document provides an overview of SPAs and discusses development tools and techniques for building SPAs using ASP.NET and common JavaScript frameworks.