‘Circularity’ is the story of a Janus-faced conceptual structure, that on the one hand led to deep scientific discoveries, and on the other hand is used to trick the mind into believing the impossible. Alongside mathematical revolutions that eventually led to the invention of the computer, the book describes ancient paradoxes that arise from circular thinking. Another aspect of circularity, its ability to entertain, leads to a surprising insight on the time old question ‘What is humor’. The book presents the ubiquity of circularity in many fields, and its power to confuse and to instruct.See Press Release: Vicious circles — confusing, instructive, amusing?