This survey of the literature summarizes and reflects on research findings regarding elementary preservice teachers' (PSTs') mathematics conceptions and the development thereof. Despite the current focus on teacher education, peer-reviewed journals offer a surprisingly sparse insight in these areas. The limited research that exists chiefly presents views of PSTs' reasoning at singular points during a term, thus focusing on conceptions almost to the exclusion of their development. We summarize the current findings, which are a beginning of a collective understanding of PSTs' mathematical content knowledge. We believe much more work is needed to understand how PSTs can best develop their content knowledge. This is a call to the community to produce such peer-reviewed research. [Contributions to this article were provided by: Krista Strand, Fatma Aslan-Tutak, Cyndi Edgington, Crystal Hill, Patrick M. Kimani, Briana Mills, Dana E. Olanoff, George Roy, and Jennifer Tobias.]