Hello Agents is a comprehensive open-source tutorial by Datawhale (datawhalechina) for building AI agents from first principles. Spanning 16 chapters organized into five progressive learning modules, it covers agent theory, LLM foundations, and practical multi-agent implementation. The project includes a self-developed HelloAgents framework built on OpenAI APIs, with hands-on examples using LangGraph, AutoGen, and AgentScope. Advanced topics include memory systems, RAG with vector storage, MCP (Model Context Protocol), context engineering, and Agentic RL training pipelines from SFT to GRPO. Real-world case studies feature travel assistants, research agents, and multi-agent simulations. With 23,100+ stars, 57 contributors, and 690 commits, it has become one of the most popular agent learning resources in the open-source community.