The regulation of sexual reproduction in yeast constitutes the highest level of differentiation observed in these unicellular organisms. The various ramifications of this system involve DNA rearrangement, transcriptional control, post-translational modification (such as protein phosphorylation) and receptor/signal processing. A few basic similarities are common to both fission and budding yeasts. The wiring of the regulatory circuitry, however, varies considerably between these divergent yeast groups.