LangChain is an open-source developer framework that simplifies building applications powered by large language models. It provides standard abstractions and interoperable components for models, embeddings, vector stores, chains, agents, and retrieval-augmented generation (RAG). LangChain integrates with many LLM providers, vector databases, and third-party tools, and includes higher-level tooling (like LangGraph) for orchestrating controllable agent workflows and multi-step reasoning. Its value is in enabling developers to connect LLMs to external data, APIs, and application logic in a modular, production-ready way that supports multi-language SDKs and community extensions.