Platelets are anucleate cells that circulate throughout the bloodstream. They are equipped with complex membrane proteins that bind to damaged blood vessels, receptors that trigger activation, and granules that release coagulation factors upon activation. While their primary role is hemostasis, platelets also interact closely with immune cells, circulating tumor cells, and infectious bacteria. These unique properties have inspired many biomaterial designs and new cell engineering approaches for drug delivery. In this chapter, we review engineered platelets not only with enhanced coagulation capabilities, but also with new functions such as tumor targeting and delivering non-native proteins. We examine the in vitro production of these platelets, including nanoparticle modifications and genetic engineering. We also discuss the impact of engineered platelets on new therapy development and approaches for their mass production.