The similarity between objects is judged in a wide variety of contexts from visual search to categorization to face recognition. There is a correspondingly rich history of similarity research and many known behavioral trends and models of similarity. Nevertheless, most similarity behaviors have been identified and tested only in a comparatively narrow set of unique contexts. This leaves open the question of the extent to which similarity judgments rely on common processes or resources and the specific nature of those processes if so. We tested three diverse yet well-established measures of object similarity using identical, psychometrically controlled stimuli and identical analyses across tasks. We found several consistent behavioral effects across tasks that provide clues as to the nature of task-general similarity processes and serve as diagnostic targets for computational models of similarity.