Running Lean, by Ash Maurya, is a guide for startups focusing on iterative development and customer validation. The book utilizes the Lean Canvas framework for business model development and emphasizes testing assumptions through experiments, customer interviews, and data analysis. It covers prioritizing risks, building minimum viable products (MVPs), and achieving product/market fit. The provided text includes excerpts showcasing endorsements, the book's structure, and detailed explanations of the methodologies used.