It is widely believed that metacognition is a specialized cognitive capacity that only humans possess. A contentious debate in the field of comparative psychology is whether animals have metacognition. The exploration of this question will help researchers to uncover the phylogenetic roots of metacognition and to map the evolutionary history of higher cognitive functions in humans. This article reviews the main animal metacognition studies in the past 25 years. We summarize three common research paradigms and corresponding measures: uncertainty monitoring, information seeking, and confidence judgment paradigms. Two opposing explanatory tendencies and their rationales are outlined in the field of animal metacognition research: associative and metacognitive models. In response to the debate between associative and metacognitive models, two future research orientations are proposed to improve the research paradigm to assess the metacognitive model and to innovate theory to integrate these models into a new one.