Six experiments were conducted on the effects of expertise on basic-level categorization. Individuals with varying levels of knowledge about songbirds generated lists of attributes, named objects, identified and discriminated among object silhouettes, verified category membership at 4 hierarchical levels, and visually identified songbirds primed either by species-specific, related, or unrelated birdsong. Results indicated that the original basic level never lost its privileged status. Expertise increased access to categorical information at the subordinate level for intermediate experts and at both the subordinate and sub-subordinate levels for advanced experts, causing these sublevels to function as basic. Throughout the continuum of expertise, conceptual knowledge interacted with perception. Accordingly, experts attended to different and more subtle perceptual features than novices.Whether one is an expert birder, tropical fish hobbyist, mineralogist, or a 5-year-old dinosaur enthusiast, a critical aspect of expertise acquisition involves categorizing and naming the objects within the expert domain. An important empirical question concerns the outcome of this heightened knowledge of category names and attributes. Is there one universal level of abstraction at which all individuals find it most useful to think about objects because of the perceptual information available in the natural world? Or do experts and novices naturally think about objects at different levels of specificity? This question has intrigued both psychologists and cognitive anthropologists for several decades and has led to a great deal of theorizing in both disciplines concerning the degree to which categorization is a constructive process. The aim of the present research was to determine to what extent the universal level of abstraction maintains its primacy throughout the continuum of expertise by