What is the foundational idea in agile software delivery? For me at least it is the idea that requirements for change in a system can be delivered one by one. The implications of this idea are far reaching, not least in the ability to track how those requirements change as the world changes. Yet too often those seeking to change to agile miss the difficult step, the prerequisite without which the pay-off of agility is unattainable. They adopt a methodology that provides the framework for the interaction of teams and business, tracking progress and quantifying velocity without seeing that the one-by-one idea has changed things (or it needs to change things) at a much more fundamental level. Without being able to integrate, test and deliver each of the myriad of small changes reliably and - most importantly - rapidly/cheaply, this idea is uneconomic. If we are building, integrating, testing and deploying systems manually we cannot do it for every small change. We have to revert to a change-freeze and a batch process for stabilisation and release.
So - back to this book. Why is it so important?
What Jez Humble and David Farly have done is provide a detailed and practical guide for teams to provide the foundation for their agile process. They could have written a shorter book and if they had I guess even more people would read it, but it would not have been so useful to this essential process in adopting agile - integrate, test, deliver every incremental change continuously. The book is packed with practical advice, experience and discussion of individual tools and practices. Although the book is clearly targeted at practitioners and will give them a treasure store of advice to move their project and organisation forward, I believe that managers and senior executives should also study this book - if not to examine the detailed discussion on every page, at least to understand the importance and complexity of "continuous delivery" in any agile adoption, and the enabling technologies that release its power. Continuous delivery is an aspiration. It's an assymptote that may approach the ideal but never attain it. So even if you have started down the route that Jez and David have outlined, you will find much here to inspire and guide your continuing journey. But if you still think agile development is only about defining and prioritising stories, and that continuous integration and automated build, testing and deployment are optional extras, you need to read this book now, before you waste an awful lot more of your company's money.