The world of technology is constantly evolving and, with it, so are the methodologies that guide how we develop and manage these technological advancements. Agile methodologies have taken the software development world by storm, offering flexible and efficient ways to handle complex projects in a rapidly changing environment. Yet, there has been a conspicuous gap in the application of Agile methodologies to one particular area of technology - mainframes. Mainframes are the bedrock of global IT infrastructure. They process 30 billion transactions per day, including 90% of all credit card transactions. They host the core business systems of 71% of global Fortune 500 companies. Despite their widespread use and critical importance, mainframes have, until recently, been untouched by many of the advancements in software development methodologies. In many organizations, mainframe systems development continues to follow the classic Waterfall model, which is often perceived as a safer and more reliable approach. This book, "Agile Ascendancy: Modernizing Mainframe Development," seeks to bridge the gap between the world of Agile methodologies and mainframes. It is designed as a guide to help mainframe professionals understand and implement Agile methodologies, even within the constraints that mainframe environments might impose. The journey to Agile transformation is not an easy one, particularly in an environment as unique and complex as mainframes. Yet, it is a journey worth embarking on, for the benefits of Agile methodologies are as applicable to mainframes as they are to any other area of software development. This book seeks to take you on that journey, providing guidance, insights, tools, and real-life case studies to help illuminate the path. From introducing the Agile principles to delving into specifics of implementing Agile on mainframes, this book aims to be a comprehensive guide for both novices and experienced professionals in the Agile and mainframe space. It covers a wide range of topics, from cultural changes, process transformations, and technical adaptations, providing a holistic view of the Agile transformation process. Whether you're a project manager, a developer, a business analyst, a tester, or an executive, this book has something for you. It is designed to be a roadmap, a toolkit, and a source of inspiration as you undertake the transformation towards Agile in your mainframe environment. Join us in this journey towards modernizing mainframe development and uncovering the latent potential of Agile methodologies in transforming the way we manage and develop our most critical business systems.