This book presents a set of formal requirements-explicit, executable instructions-for systems engineering and architecting. Written in Mathematica®, the requirements provide tools to help systems engineers and architects accomplish key tasks better, faster, and cheaper. Chapters open with real-world case studies and illustrate using formal requirements to accomplish four key activities: model system behavior, make decisions, establish natural language requirements, and improve processes. Each chapter ends with heuristics that serve as guiding principles for doing systems engineering and architecting. The formal requirements are available online as an open source library.