In this paper, we critically analyze how the concept of negative knowledge contributes to the understanding of professionals' expert practice and learning. Negative knowledge is experientially acquired knowledge about what is wrong and what is to be avoided during performance in a given work situation. In terms of its theoretical foundation, the concept relates to constructivist theorization and metacognition. Building on existing conceptions of negative knowledge, we systematically relate the concept to research on expertise and learning from errors. The concept of negative knowledge augments existing theories of professional knowledge by emphasizing knowing about what to avoid as part of experts' effective actions. During routine actions, negative knowledge enhances professionals' certainty of how to proceed and increases the efficacy through the avoidance of impasses and suboptimal problem-solving strategies. Quality and depth of reflective processes after actions are related to the development of negative knowledge. The potential of negative knowledge for the investigation of professional learning is discussed through reference to recent empirical work.