LangChain is an open-source framework that simplifies the development of applications using large language models (LLMs). It offers tools and abstractions to enhance the customization, accuracy, and relevancy of LLM-generated information. LangChain allows developers to connect LLMs to external data sources, and create applications like chatbots, question-answering systems, and virtual agents. Key components include model interfaces, prompt templates, chains, agents, retrieval modules, and memory. LangChain enables the creation of complex, context-aware applications by combining different components.