In this issue, Schwikowski et al. (see p. 1257) compile 2,709 protein–protein interactions from the yeast community and determine that these interactions form a large network of 2,358 interactions among 1,548 proteins, and several smaller networks. This map provides an intriguing starting point for assigning functions to uncharacterized proteins, by tracing their interacting partners back to proteins with known activities. It also provides a glimpse into how protein interactions can unexpectedly span cellular processes and compartments. The map will take on added dimensions as the functions of now uncharacterized proteins are added, and as the approach is applied to other organisms, allowing cross-referencing of protein interactions across a spectrum of species (see also p. 1242).