Applications talk to each other through API. It is API that enables websites to use Google Maps and establish real time interface with Facebook, for example. However, APIs also set the level of interface and draw the line beyond which an accessing application cannot go.  By limiting access, APIs protect proprietary code, at least to some extent.

Today, the majority of operating environments provide programmers access through APIs. Web APIs allow access to already established infrastructure, thus enabling third party programmers to create software to fulfill niche needs of end users and program solutions that fill in the gaps where required.

Application programming interfaces save time in software development and provide the means to link mobile apps together to perform various functions without the need to write new code to do things that are already being done. It isn’t necessary to reinvent the wheel each time. It is this quality that is the single biggest driver of mobile apps. It enables people to carry considerable computing power in their pockets without the need to carry the computer itself. It’s there in the cloud, on the Web or available for download. API is there to link applications together across digital space and provide the means to build a digital world out of many separate pieces.