Animal germ cells differentiate as sperm or eggs, depending on their sex. Somatic signals tell germ cells whether they reside in a male or female body, but how do germ cells interpret those external cues to acquire their own sexual identity? A critical aspect of a germ cell's sexual puzzle is that the sperm/egg decision is closely linked to the cell-cycle decision between mitosis and meiosis. Molecular studies have begun to tease apart the regulators of both decisions, an essential step toward understanding the regulatory logic of this fundamental question of germ cell biology.