This document introduces API Platform, an open-source PHP framework for building web APIs. It provides out-of-the-box features like JSON-LD support, Swagger documentation, and a fully-featured UI. API Platform is built on Symfony and uses Doctrine ORM by default. It allows developers to quickly create RESTful APIs from PHP entities with automated CRUD functionality. The framework also supports content negotiation, filtering, embedded relations, and has a growing community of contributors.