DMN is the standard for model-based decision automation. Using standardized diagrams and tables together with the Low-Code expression language FEEL, DMN empowers both business and technical users to decompose complex decision logic into transparent and easily maintained models that can be instantly deployed as executable REST services. Moreover, it is a vendor-neutral standard maintained by the Object Management Group, so models behave the same in any compliant tool. Using a combination of logic decomposition diagrams (DRDs), standard tabular formats (boxed expressions), and the Low-Code expression language FEEL, DMN allows subject matter experts to automate the operational decisions that drive the business. More powerful and business-friendly than Microsoft Power FX, DMN is used by both business and technical modelers to create, test, and deploy cloud-based decision services. This book provides a comprehensive guide to the language, completely revised from the 2nd edition, and updated to the current draft DMN 1.6 version. It includes many practical examples, with 271 diagrams and tables. Part I is the business-oriented Guide to Decision Modeling, explaining the creation and use of Decision Requirements Diagrams, decision tables, and all the tabular boxed expression types, as well as a deep dive into all the FEEL functions and operators. Part II is the more technically oriented DMN Cookbook (formerly a separate book), updated to DMN 1.5/1.6, with solutions to over 40 modeling challenges.