Although preservice elementary school teachers (PSTs) have been shown to lack the understanding of multidigit whole numbers necessary to teach in ways that empower students mathematically, little is known about their conceptions. I draw upon the extensive research on children's understanding of multidigit whole numbers to explicate PSTs' conceptions of these numbers. I develop a framework for PSTs' conceptions of multidigit whole numbers and use that framework to describe their conceptions and their difficulties in the context of the standard algorithms. I then link the PSTs' conceptions in the context of the standard algorithms to their performance in other contexts.