This book explores the cultural figure of the algorithm as it operates through contemporary digital culture. Drawing on sources that range from Neal Stephenson’s Snow Crash to Diderot’s Encyclopédie, from Adam Smith to the Star Trek computer, it explores the gap between theoretical ideas and pragmatic instructions. Humans have always believed that certain invocations—the marriage vow, the shaman’s curse—do not merely describe the world but make it. This book argues that the algorithm—in practical terms, “a method for solving a problem”—has its roots not only in the mathematical concept of “effective computability” but also in cybernetics, philosophy, and magical thinking. After bringing the full history of the term into view, the book describes how the algorithm attempts to translate between the idealized space of computation and a messy reality, with unpredictable and sometimes fascinating results. Case studies of this implementation gap include the development of intelligent assistants like Siri, Google’s goal of anticipating our questions, the rise of algorithmic aesthetics at Netflix, Ian Bogost’s satiric Facebook game Cow Clicker, Uber’s cartoon maps and black box accounting, and the revolutionary economics of Bitcoin. If we want to understand the gap between abstraction and messy reality, we need to build a model of “algorithmic reading” and scholarship that attends to process as part of a new experimental humanities.