The book presents both the current state of the art in requirements engineering and a systematic method for engineering high-quality requirements, broken down into four parts. The first part introduces fundamental concepts and principles including the aim and scope of requirements engineering, the products and processes involved, requirements qualities to aim at and flaws to avoid, and the critical role of requirements engineering in system and software engineering. The second part of the book is devoted to system modeling in the specific context of engineering requirements. It presents a multi-view modeling framework that integrates complementary techniques for modeling the system-as-is and the system-to-be. The third part of the book reviews goal-based reasoning techniques to support the various steps of the KAOS method. The fourth part of the book goes beyond requirements engineering to discuss the mapping from goal-oriented requirements to software specifications and to software architecture. Online software will accompany the book and will add value to both classroom and self-study by enabling students to build models and specifications involved in the book's exercises and case studies, helping them to discover the latest RE technology solutions. Instructor resources such as slides, figures and handouts are available from an accompanying website.