If you have observed newly developed technologies, one thing that sets them apart is their user-friendliness. Gone are the days when only geeks could operate computers. Software development has made it easier for users to operate computers, cell phones, and other products. It is perfectly possible for you to use the Internet, without knowing what Application Programming Interfaces (APIs) are or how the Internet works. However, if you want to truly appreciate its working, you must know what they are. They are a software construct which makes it easy for web services to be offered on the Internet. How Does it Work? Many years ago, before the development of the world wide web and even in its early years of development, there was a major disconnect between different software developers, which slowed down development of applications. Each company protected its code and developed all the software that is required to bring out its products. The need to develop all software tools from ground up, meant that a lot of time and effort would be devoted in creating a platform, on which the software could be used. However, this closed world, divided by walls of secrecy, slowly gave way to sharing and collaboration. A closed world rarely grows beyond certain limits. Platform independence and the need to provide web services, brought about the need to develop interfaces which could enable different applications to communicate on the Internet. Software companies realized that by opening their software platform to be shared, they could profit from the development effort of external sources and provide web-based applications at lesser cost and with more efficiency. This is what led to the development of the API. One could define it as a complete set of programming constructs that enables developers on the Internet, to access and integrate with web-based applications. The programming constructs, that are part of an API, include protocols, data structures, tools, and various routines that enable interaction between the web-based application and other subsidiary software constructs. The function of the interface is that of an interpreter or mediator between different software programs. This helps certain applications on the Internet, to take advantage of previously built programs. One need not start building any program from square one. More generally, it may be like a software development platform for third-party developers and an interface for bringing about interaction between programs. An API token or key is a password used by the company, to validate user identity and prevent misuse. An API call is essentially a way of connecting to a web-based service, using code developed on its platform. For example, Apple computers has developed and shared its API for the iPhone with developers, to help them create iPhone apps. Similarly, all the major software developers release their interfaces to external developers, to help them create applications for the platform created by them. An API is basically a communicating medium for software programs of different types, to work together. The interface itself remains in the background and is generally not visible to a user on the Internet. When you make any online transaction like buying books on Amazon or use Twitter through your Android phone, APIs are functional in the backdrop, making all these web services available. Thus, these interfaces have helped synergize software resources to provide platform-independent web services. If it wasn't for APIs, the web services which make life so much easier for netizens, would be non-existent.