How to build SEO friendly Single Page Applications?

What is a Single Page Application (SPA)?

A Single Page Application (SPA) is a website which fits in only one HTML page. In such sites, every click on internal links are intercepted by the JavaScript code in order to retrieve contents in background and display them in the page without reloading it. To achieve this, contents are retrieved dynamically by using Ajax. You can read this article if you want to know how Ajax can improve the user experience.