In biology, phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms (e.g., species or populations). Today, molecular phylogenetics is the modern technique used to assist in the classification of biological systems. Platelets, despite their small size and lack of a nucleus, are highly complex and serve multiple functions. In the animal kingdom, platelets are unique to mammals. This chapter provides a brief overview of the phylogeny of blood platelets.