The use of outline shape in recognizing objects was investigated in 4 experiments. In Experiment 1, participants matched a shaded image to either another shaded image or a silhouette. In Experiment 2, they initially named shaded images; later they named either shaded images or silhouettes. Performance in both experiments was predicted by changes in the outline shape of the stimuli. The same matching (Experiment 3) and priming (Experiment 4) paradigms were then used to investigate recognition with objects that were rotated between presentations so as to change the outline shape of the object. Recognition was predicted by changes to outline shape. These results place constraints on models of object recognition and are most compatible with viewpoint-dependent models of recognition.