LangChain is a modular framework that helps developers create advanced AI applications by connecting large language models with external data sources and tools. It provides chain abstractions for sequential LLM calls, agent orchestration for decision-making workflows, memory modules for context retention, and integrations with document loaders, vector stores, and API-based tools. With support for multiple providers and SDKs in Python and JavaScript, LangChain accelerates the prototyping and deployment of chatbots, QA systems, and personalized assistants.