This book serves as a text for an introductory course on the organisation of digital computers and their programming in assembly language. The book emphasises the general principles and concepts of machine-level organisation and programming, placing these in the context of an overall understanding of computer systems and software. General themes are illustrated using the MC68000 processor, and the book provides all the reference information necessary for an introduction to 68000 assembly-language programming. The only prerequisite is an elementary understanding of computer programming in a high level language.