Peter James Denning (born January 6, 1942) is an American computer scientist and writer. He is best known for pioneering work in virtual memory, especially for inventing the working-set model for program behavior, which addressed thrashing in operating systems and became the reference standard for all memory management policies. He is also known for his works on principles of operating systems, operational analysis of queueing network systems, design and implementation of CSNET, the ACM digital library, and codifying the great principles of computing. He has written numerous influential articles and books, including an overview of fundamental computer science principles, computational thinking, and his thoughts on innovation as a set of learnable practices.

Denning was born January 6, 1942, in Queens, New York, and raised in Darien, Connecticut. He took an early interest in science, pursuing astronomy, botany, radio, and electronics while in grade school. At Fairfield Prep, he submitted home-designed computers to the science fair in 1958, 1959, and 1960. His second computer, which solved linear equations using pinball machine parts, won the grand prize.

He attended Manhattan College for a Bachelor in EE (1964) and then MIT for a PhD (1968). At MIT he worked on Project MAC and contributed to the design of the pioneering Multics operating system. His PhD thesis, "Resource allocation in multiprocess computer systems", introduced seminal ideas in working sets, locality, thrashing, and system balance.

At Princeton University from 1968 to 1972, Denning wrote his classic book, Operating Systems Theory (1973), with E G Coffman. He collaborated with Alfred Aho and Jeffrey Ullman on optimality proofs for paging algorithms, and on a simple proof that compilers based on precedence parsing do not need to backtrack. At Purdue University (1972–1983) he supervised numerous PhD theses validating locality-based theories of memory management and extending the new mathematics of operational analysis of queueing networks. He co-founded CSNET. He became department head in 1979 and completed another book on computational models, Machines, Languages, and Computation, with Jack Dennis and Joe Qualitz.

At NASA Ames from 1983 to 1991, he founded the Research Institute for Advanced Computer Science (RIACS) and turned it into one of the first centers for interdisciplinary research in computational and space science.

At George Mason University from 1991 to 2002 he headed the Computer Science Department, was an associate dean and vice provost, and founded the Center for the New Engineer. The Center was a pioneer in web-based learning. He created a design course for engineers, called Sense 21, which was the basis of his project to understand innovation as a skill. He created a course on Core of Information Technology, the basis of his Great Principles of Computing project.

At Naval Postgraduate School since 2002, he heads the Computer Science Department, and directs the Cebrowski Institute for Innovation and Information Superiority. He chaired the faculty council.

Denning has served continuously as a volunteer in the Association for Computing Machinery (ACM) since 1967. In that time, he served as president, vice president, three board chairs, Member-at-Large, Editor of ACM Computing Surveys, and Editor of the monthly ACM Communications. He received seven ACM awards for service, technical contribution, and education. ACM presented him with a special award in June 2007 recognizing 40 years of continuous service.