Three of the most important questions concerning actin function are: (a) How does actin structure relate to actin function? (b) How does each of the numerous proteins that interact with actin contribute to actin cytoskeleton function in vivo? (c) How are the activities of these proteins regulated? Powerful molecular genetics combined with well-established biochemical techniques make the yeast Saccharomyces cerevisiae an ideal organism for studies aimed at answering these questions. The protein sequences and biochemical properties of actin and its interacting proteins and the pathways that regulate these interactions all appear to be conserved, indicating that principles elucidated from studies in yeast will apply to all eukaryotes. In this review, we highlight advances in our general understanding of actin properties, interactions with other proteins, and regulation of the actin cytoskeleton, derived from studies in the budding yeast S. cerevisiae.