Mathematics anxiety, like all emotions, is an emergent construction, progressively elaborated and refined through iterative cognitive appraisals of environmental stimuli and somatic states. We synthesize contributions in the areas of emotion, identity, goal theory, and Piaget’s genetic epistemology to propose a theory of the cognitive antecedents of mathematics anxiety. Based on this synthesis, we recommend design principles for online learning environments to minimize students’ anxiety by purposefully affecting the cognitive appraisals and constructions that contribute to its emergence.