This guidebook offers a pragmatic roadmap that helps teams scale agentic AI across the enterprise, including digital product development. Part 1 follows a structured seven-day arc to guide professionals through RE fundamentals--elaboration, documentation, quality assurance, and ongoing management--while showing where GenAI adds real value. It contrasts agile and waterfall approaches and grounds theory in practice-ready examples. Part 2 explores the evolution of AI into the agentic era, emphasizing trustworthy and green AI as pillars for responsible adoption. It presents a playbook for scaling beyond pilots, reshaping operating models, and embedding agent engineering. A novel product-by-development-process matrix illustrates how agentic technologies enhance both digital products and the way they are built. This book is specially designed to address the needs of product managers, requirements engineers, enterprise architects, and digital transformation leaders.