Social theory has provided a useful framework for research with microorganisms. Here I describe the advantages and possible risks of using a well-known model organism, the unicellular yeast Saccharomyces cerevisiae, for sociobiological research. I discuss the problems connected with clear classification of yeast behaviour based on the fitnessbased Hamilton paradigm. Relevant traits include different types of communities, production of flocculins, invertase and toxins, and the presence of apoptosis.