This YouTube video provides a tutorial on Langchain's Expression Language (LCEL), a declarative way to build chains of components (LLMs, prompts, tools, etc.) for applications. The video contrasts LCEL with older Langchain chaining methods, demonstrates LCEL's features (streaming, async support, parallel execution, runnables), and shows practical examples, including RAG pipeline integration. The presenter emphasizes practical application over deep theoretical explanations.