Some accounts imply that basic-level emotion categories are acquired early and quickly, whereas others imply that they are acquired later and more gradually. Our study examined this question for fear, happiness, sadness, and anger in the context of children's categorization of emotional facial expressions. Children (N=168, 2-5 years) first labeled facial expressions of six emotions and were then shown a box and asked to put all and only, e.g., scared people in it. Before using fear in labeling, children had begun to include "fear" faces and to exclude other (especially positive) faces from the fear box/category; after using fear, children continued to include other (especially negative) faces. The same pattern was observed for happiness, sadness, and anger. Emotion categories begin broad, including all emotions/faces of the same valence, and then gradually narrow over the preschool years. (Contains 1 table and 5 figures.)