The Caenorhabditis elegans germ line provides an exceptional model for analysis of the molecular controls governing stem cell maintenance, the cell cycle transition from mitosis to meiosis, and the choice of sexual identity-sperm or oocyte. Germline stem cells are maintained in an undifferentiated state within a well-defined niche formed by a single somatic cell, the distal tip cell (DTC). In both sexes, the DTC employs GLP-1/Notch signaling and FBF/PUF RNA-binding proteins to maintain stem cells and promote mitotic divisions, three additional RNA regulators (GLD-1/quaking, GLD-2/poly(A) polymerase, and GLD-3/Bicaudal-C) control entry into meiosis, and FOG-1/CPEB and FOG-3/Tob proteins govern sperm specification. These key regulators are part of a robust regulatory network that controls germ cell proliferation, stem cell maintenance, and sex determination. Parallels with controls in other organisms include the use of PUF proteins for stem cell maintenance and the prominence of mRNA regulation for the control of germline development.