This book, Building Evolutionary Architectures, explores how to design software systems that can adapt to changing requirements and technologies. It introduces the concept of "fitness functions" as automated mechanisms to govern architectural characteristics and guide incremental change. The authors emphasize the importance of appropriate coupling, well-defined contracts, and automated verification to enable evolvability. They discuss various architectural patterns, data management strategies, and organizational considerations for building such systems. Furthermore, they provide real-world case studies and practical guidelines to help architects implement evolutionary architecture principles effectively. The text also presents common pitfalls and antipatterns to avoid when building these architectures. Ultimately, the book advocates for a shift towards more adaptable and resilient software systems that can thrive in dynamic environments.