Messy systems slow progress and increase costs--but tidying up isn't just an individual effort, it's a team responsibility. In this essential guide, author Kent Beck offers a practical framework for improving system design collaboratively. Building on the ideas from Tidy First? , this book shows teams how to balance changes to a system's behavior with improvements to its structure, ensuring smoother development, faster progress, and more effective collaboration. With a focus on teamwork, this book emphasizes not just fixing code but strengthening the human relationships that sustain system evolution. Through thoughtful insights, real-world examples, and actionable practices, Beck teaches teams to alternate between tidying and building, minimizing risk while maintaining momentum. Learn how to make large changes safely, refine your team dynamics, and clear the path to sustainable system improvements with approaches that prioritize both people and code. Whether you're an individual contributor or leading a design team, you'll be equipped to design better systems--together. Understand the difference between changes to system behavior and structure Learn the power of alternating investments between tidying and building Apply small, safe steps to execute large system changes Strengthen team relationships to sustain healthy design practices Prepare for design challenges shaped by diverging incentives and human collaboration.