LangChain

LangChain is the most widely-adopted framework for building applications powered by large language models (LLMs). It provides a standard interface for chains (sequential LLM calls), agents (autonomous decision-making), and memory (conversation history). In 2025, LangChain 1.0 brought production stability with standardized content blocks, simplified package structure, and enhanced middleware. LangGraph enables complex state machine workflows for advanced agent behaviors. Integrates with all major LLM providers (OpenAI, Anthropic, Google, Mistral), vector databases, and tools. LangSmith provides observability and debugging for production applications. Used by Uber, LinkedIn, Klarna, and JP Morgan. Available in Python and JavaScript. Essential framework for developers building chatbots, RAG systems, and AI agents.