You hold in your hands a comprehensive guide to creating a flourishing software development practice - one that makes a powerful impact with the software it builds. This guide describes the unique aspects of creating software-based products. It also lays out the clear practical guidance that's necessary to construct and evolve a modern practice. This includes hiring, structuring teams properly, writing good code, leveraging test-driven development, designing architecture, automating development processes with DevOps techniques, and - importantly - leading teams through the disruptive change that each of these can represent. Further, the first principles upon which these practices rest will be elaborated so that the reader can readily adapt the already practical techniques to the broadest possible set of real-world situations.