To better understand how comparison can be effectively used in mathematics instruction, we reviewed research in psychology and education, with the aim of identifying types of comparison that take place in mathematics learning, and considering the effects of comparison on procedural and conceptual understanding. We identified three types of comparison that are commonly utilized in mathematics instruction and learning: (1) problem-to-problem comparisons, (2) step-to-step comparisons, and (3) item-to-abstraction comparisons. Of these three types, only the effects of problem-to-problem comparisons on learning have been well documented. This paper therefore highlights the need for further research to elucidate the unique contributions of different types of comparison in mathematics learning.