Composite Software offers a new level of granularity when compared to SaaS (Software as a Service). Composite Software is about enabling "right-sourcing", i.e. move (or keep) arbitrary small or large elements of functionality wherever it is the most cost effective to operate them, not just entire systems. Economically, "right-sourcing" is far more efficient than "outsourcing" and SaaS. Despite the tremendous benefits of composite software, the software industry is holding back the development of a composite programming model though major pieces of the model have been realized recently. The goal of this book is start by understanding today's software construction processes and technologies and explore why and how it should be evolved to support core composition mechanisms.