LangGraph is a library to help developers build multi-actor, multi-step, stateful LLM applications by providing a coordination layer to define actors and their interactions, schedule execution, model the back-and-forth between multiple actors, and update a central state. This enables human-in-the-loop features such as Interrupt and Authorize, which allow users to control the application's output in real-time or define specific points where they want to intervene. With LangGraph, developers can build complex LLM applications that require human supervision or approval, making them more useful in the real world.