In the 2018-2019 academic year, more than 560,000 prospective teachers attended more than 21,500 teacher preparation programs (TPPs) housed in more than 2,100 institutions in the United States. Some will either never complete their program or fail to seek or secure teaching positions, but the majority will, and they will become a substantial part of the future U.S. teacher workforce. But what is known about these teacher candidates? Who are they? Where do they come from? Why are they attracted to teaching? What factors shape enrollment and completion patterns across the diverse set of programs that constitutes our current system of teacher preparation? The answers to these questions are crucial to efforts designed to enhance the U.S. teacher workforce; local efforts to improve programs; state and national policies concerning teacher quality; and the collective understanding of how teacher supply and demand is both forged by and reflects economic, social, historical, and cultural trends. The purpose of this paper is to describe the current landscape of candidates applying to and enrolling in TPPs, and to summarize what is known about who pursues teacher certification. To this end, it examines (1) the large-scale data available on TPPs; and (2) culled additional data from historians' analyses of the teacher workforce, contemporary large-scale studies of TPPs, papers on local design and program histories, and case studies of particular programs as well as examining information on programmatic innovation in local contexts. Here the paper summarizes efforts--through programs and policies--to recruit new candidates to the teacher workforce.