Welcome to 'Encapsulating Legacy: A Guide to Service-Oriented Architecture in Mainframe Systems'. This book is a comprehensive exploration of the intersection between the enduring world of mainframe computing and the dynamic landscape of service-oriented architecture (SOA). It is intended for IT professionals, systems architects, and decision-makers who are navigating the challenging yet essential path of modernizing legacy mainframe systems. The journey of mainframe modernization is not merely a technological upgrade; it’s a strategic transformation that affects every facet of an organization’s IT infrastructure. This book aims to demystify the process and principles of integrating SOA into mainframe environments, addressing both the technical and strategic aspects of such an endeavor. In the following chapters, we delve into the fundamentals of SOA, its relevance to mainframes, and the practical steps involved in implementing this architecture in a mainframe context. We cover a range of topics from assessing your current infrastructure, planning, and executing the migration, to managing the new environment effectively. Additionally, we explore the critical aspects of security, compliance, and quality assurance in these modernized systems. Real-world case studies are included to provide insights into successful implementations and the lessons learned from them. We believe these stories will not only inform but also inspire you as you embark on or continue your journey in mainframe modernization. As you turn the pages, we hope you find this book to be both a valuable guide and a source of inspiration. The path to modernizing mainframes with SOA is complex and challenging, but with the right approach and understanding, it can lead to significant benefits for your organization. We wish you success on your journey towards encapsulating your legacy systems into a more flexible, efficient, and future-ready IT landscape.