LangChain is a Python framework for building applications powered by language models. It provides abstractions for common patterns: chaining multiple LLM calls, connecting AI to external tools, managing conversation memory, and building retrieval-augmented generation (RAG) systems.
You need LangChain when your AI application requires more than a single API call: multi-step reasoning, tool use (search, calculate, query database), document retrieval, or autonomous agent behavior. For simple API integration, direct LLM integration is simpler and faster.