This text identifies, examines, and illustrates fundamental concepts in computer system design that are common across operating systems, networks, database systems, distributed systems, programming languages, software engineering, security, fault tolerance, and architecture. Through carefully analyzed case studies from each of these disciplines, it demonstrates how to apply these concepts to tackle practical system design problems. To support the focus on design, the text identifies and explains abstractions that have proven successful in practice such as, remote procedure call, client/service organization, file systems, data integrity, consistency, and authenticated messages. Most computer systems are built using a handful of such abstractions. The text describes how these abstractions are implemented, demonstrates how they are used in different systems, and prepares the reader to apply them in future designs. *Formulates and illustrates the main principles of computer system design. *Presents a cross-disciplinary approach drawing on examples from networking, operating systems, distributed systems, architecture and other disciplines within computer science. *Explores principles and abstractions in-depth with numerous case studies, including Unix (file systems); URL, DNS (naming); NFS (client/service); virtual machines (virtualization); disk arms (scheduling); TLS (security). *Illustrates core concepts using numerous pseudocode examples throughout the text. *Supports on-line open educational resources that include several additional chapters and problem sets, plus MIT Open CourseWare materials, including lecture videos.