In this paper, we consider the impact of cognitive illusions on decision making in the operations management field, in areas ranging from product and process development to project management. Psychologists have studied the effects of overconfidence, the planning fallacy, illusions of control, anchoring, confirmation bias, hindsight bias, and associative memory illusions on individual judgment, thinking, and memory in many experiments, but little research has focused on operations management implications of these biases and illusions. Drawing on these psychological findings we discuss several of these cognitive illusions and their impact on operations managers, plant workers, technicians and engineers alike in a variety of operational settings. As in other contexts, these cognitive illusions are quite robust in operations management, but fortunately the impact of selected illusions can be substantially reduced through debiasing techniques. The examples discussed in this paper highlight the need for more operations-management-based research on the impact of cognitive illusions on decision making.