In the Scientific Revolution the concept of body evolved along several divergent lines, from conceptions that rely exclusively on extension and motion to more elaborate accounts that include attributes such as solidity and force. A host of complications were disputed, such as atomism versus the infinite divisibility of bodies, the distinction between primary and secondary properties, and the possibility of a vacuum. This chapter explores these and other issues, but with an emphasis on the relationship between body and spatial extension. Descartes's three-part distinction—i.e., whether the relationship between body and extension is conceptually, modally, or really distinct—serves as a framework for investigating the development of early modern theories of material body, a process that laid the basis for the ontology and epistemology of modern science.