PER BAK (1948-2002) was one of the founders and most influential contributors to the study of complex systems. He made many contributions to science, but the best known was a general theory of self-organization, which he called, "self-organized criticality".

Bak, who was based at Imperial College London since 2000, had been Senior Scientist in the Physics Department at Brookhaven National Laboratory. He published approximately 150 scientific articles and his work was reviewed in numerous publications including Science News, The Economist, New Scientist, Nature Physics, Today, The New York Times, and Physics World. An interview with Per Bak appeared in the Nova Series on PBS and the Discovery Channel and an audio interview is available online on The Paula Gordon Show.

He was the author of How Nature Works: The Science of Self-Organized Criticality.

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