Cell-to-cell communication in yeasts is an emerging area of research. Quorum sensing is a density-dependent, cell-to-cell communication mechanism in microorganisms. It is mediated via secretion of small diffusible molecules called quorum signals, which regulates gene expression through signal transduction pathways. Yeast quorum sensing has mostly been studied in Saccharomyces cerevisiae and Candida albicans. In S. cerevisiae, 2-phenylethanol, tyrosol, and tryptophol are the main quorum sensing molecules (QSMs); in C. albicans, farnesol and tyrosol are the main QSMs. This chapter provides examples of quorum sensing molecules in S. cerevisiae and C. albicans. In addition, it focuses on the mating process in S. cerevisiae, synthesis of QSMs, and the signaling pathways involved in the morphological switch between the yeast to hyphal form.