In order to fully understand the role that APIs play in our lives, it's important to understand how they have evolved. APIs have been around for decades, with modern web APIs first taking shape in the early 2000s. The history of APIs since that period can be roughly broken down into the following five phases:

APIs have been around almost as long as computing, but modern web APIs began taking shape in the early 2000s. A popular dissertation on REST by Roy Fielding and a handful of emerging technology companies including Salesforce, eBay, and Amazon, led to the definition of web APIs we use today.