Sweet cherry scion cultivars have been selected over millennia for many reasons, but over the past century, breeding programs have concentrated mainly on achieving improved characteristics such as yield, taste, fruit size, fruit firmness, fruit color, precocity, and resistance to fruit cracking and disease. In contrast, rootstock cultivars have only recently received attention. 'Mazzard' continues to be used widely throughout the Pacific Northwest. Over the past few decades, however, several new rootstocks have gained prominence, offering important attributes lacking in 'Mazzard'. Many of these new semi-dwarfing rootstocks, although reducing tree vigor, may impart some disease resistance, induce precocity, and enable growers to harvest premium-quality fruit from high-density orchards. This publication presents the current level of understanding of the major cherry rootstocks and links it to their performance in the Pacific Northwest.