Every day, we see content and data that comes from one source re-purposed into another. An API (Application Programming Interface) is a method for web apps, mobile apps, and websites to communicate with each other. Open APIs use a simple request/response model: a request is sent to an application, that request gets evaluated, and then the server sends a response back to the original sender.
Perhaps most importantly, APIs help to create a seamless user experience. A popular example is Facebook Connect, where signing into Facebook means you’re already authenticated when you sign up on other websites using their API. In this way, APIs are crucial for promoting conversations, integration, and sharing. And though tech giants like eBay and Amazon were among the first to use them, today even brands (e.g. ESPN, AmEx) and many startups (e.g. foursquare, Foodspotting) develop their own.