Book excerpt: "On The Foundations of Computing is a technical, historical and conceptual investigation in the three main methodological approaches to the computational sciences: mathematical, engineering and experimental. The first part of the volume explores the background behind the formal understanding of computing, originating at the end of the XIX century, and it invesitagtes the formal origins and conceptual development of the notions of computation, algorithm and program. The second part of the volume overviews the construction of physical devices to perform automated tasks and it considers associated technical and conceptual issues. We start from the design and construction of the first generation of computing machines, explore their evolution and progress in engineering (for both hardware and software), and investigate their theoretical and conceptual problems. The third part of the volume analyses the methods and principles of experimental sciences founded on computational methods. We study the use of machines to perform scientific tasks, with particular reference to computer models and simulations. Each part aims at defining a notion of computational validity according to the corresponding methodological approach"--