An API is the set of "switches and levers" that a software service exposes so that other programs and services can interact with it. You can request data from the service through its API, and with the proper permissions you use the API to send data to the service. Various software programs have had APIs of one sort or another for decades. But with the advent of Software as a Service (SaaS), and the massive proliferation of SaaS providers and increasing granularization of their offerings, APIs have taken center stage in the value chain. It feels like every piece of software, every device, every thing either has an API or will soon have one. There's a growing realization of an entire API economy, with all the trimmings: providers of core services, aggregators, utility service providers, monetization plays, registries, and of course conferences and meetups, as well as trends and initiatives such as the consumerization of enterprise APIs. It's certainly a thrill ride now in the API space, and so many new developments to write about.