This book provided a wide set of evidences fostering the understanding of how software development is structured and executed, from idea conception to the first release. The findings can be summarised as follows: focusing on limited number of suitable functionalities, and adopting partial and rapid evolutionary development approaches, early-stage software startups operate at high development speed, aided by skilled and highly colocated developers. The aim is to find early a product/market fit within extremely uncertain conditions and severe lack of resources. Nevertheless, by speeding-up the development process, startups accumulate technical debt, causing an initial and temporary drop-down in performance before setting for further growth. The conclusions can be generalised with a good degree of confidence to the majority of early-stage software startups involved in the production of innovative products, especially for web and mobile applications. Additionally we infer that more primary studies are needed in this area to support the use of scientific, engineering, managerial and systematic approaches with the aim of successfully developing software in startup companies.