Complexity can create value. At the same time, understanding more complex goods requires more of an agent’s attention. We show that equilibrium complexity is generally ine?cient when agents face competing demands on their limited attention. Because attention allocation is hump-shaped in complexity, equilibrium complexity is distorted towards inter mediate levels: well-understood goods are ine?ciently complex, whereas less well-understood goods are oversimplified. We apply our model to financial institutions facing regulatory bodies and CEOs interacting with corporate divisions.