Comparative psychology is the study of behavior and cognition across species. In recent decades, much of this research has focused on cognitive capacities that are well studied in humans. This approach provides comparative perspectives on the evolution of these cognitive capacities. Although in many areas humans shows distinct aspects of various cognitive processes, it is clear that for most major topics in human cognition, important and illustrative data are available from studies with other animals. Moreover, these areas of investigation increasingly show continuities between the behavior of other species and human behavior. Several of these cognitive processes, including concept and category learning, numerical cognition, memory, mental time travel and prospective cognition, metacognition, and language learning, highlight these continuities and demonstrate the richness of mental lives in other animals. Nonhuman animals can discriminate between categories of perceptual and conceptual classes, they can form concepts, and they can use those concepts to guide decision making and choice behavior. Other species can engage in rudimentary numerical cognition, and more importantly share with humans certain core quantitative abilities for the approximate representation of magnitude and number. Nonhuman animals share many phenomena of memory that are well-recognized in humans, and in some cases may even share the capacity to mentally re-experience the past and to anticipate and plan for the future. In some cases, some species may even reflect on their own knowledge states, memory accessibility, and perceptual acuity as they make metacognitive judgments. And, studies of animal communication provided the basis for intensive assessments of language-like behavior in certain species. Taken together, these results argue much more for continuity than discontinuity. This should not be seen as a challenge to the uniqueness of human minds, but rather as a way to better understand how we became the species we are through the process of evolution.