Sociologist Donald MacKenzie provides the most thorough and intellectually rigorous account available of how high-frequency trading and the physical infrastructure of electronic markets have transformed modern finance over the past two decades. Unlike most accounts of high-frequency trading that focus on the drama of competition between firms or the regulatory debates it has generated, MacKenzie is interested in the deeper sociological question of how the physical world — the precise locations of data centers, the speed-of-light propagation delays between cities, the choice of fiber optic versus microwave transmission — has become a determinant of competitive advantage in financial markets. Drawing on extensive interviews with practitioners, regulators, and technologists, the book traces the evolution of electronic trading from the early electronic communication networks of the 1990s through the co-location arms race of the 2000s and the microwave networks stretching between Chicago and New York and across the Atlantic. MacKenzie analyzes the social and ethical implications of a system in which competitive advantage derives almost entirely from physical proximity and communication speed rather than from information analysis or capital allocation judgment. The book also addresses the flash crash of 2010 and subsequent mini-flash crashes as evidence of emergent systemic risks in a market whose speed exceeds human supervisory capacity. Essential reading for anyone who wants to understand the material infrastructure underlying modern electronic financial markets.