As with most things in the tech world, the term API-first is a term that has taken on many meanings. And that’s okay! It really boils down to this, starting with the API and treating the API as a first-class citizen. You define and prioritize the APIs and underlying schema before you develop dependent applications, services, integrations, etc. APIs are treated as the building blocks on which the rest of your systems depend. Taking this approach generally ensures that a wide range of clients and applications can consume your API and that your app or service is compatible with a diverse number of other apps or systems. Ultimately, it provides more flexibility than some of the other popular approaches.