Much controversy still surrounds the hypothesis that the plasma membrane, which surrounds our cells, is not uniform but consists of platforms, or rafts, where proteins aggregate to perform their functions more efficiently. The controversy remains not only because the extensive evidence for the hypothesis is primarily indirect, but also because there is no good understanding of what would lead to such heterogeneity. I shall review some explanations and emphasize the role of the asymmetry of the plasma membrane. I will explicate my own view that the lipid components of the plasma membrane would form a microemulsion, will present recent experimental evidence displaying disparate behaviors, and will argue that the evidence points to a unifying picture.