We used trap associations, nest-site preferences, a food selection experiment, and measurements of nightly activity to describe resource partitioning by syntopic Peromyscus californicus and P. boylii in Monterey County, California. P. californicus and P. boylii were active over the same range of time during the night. P. boylii was caught frequently near Quercus agrifolia, nested under canopies with high densities of Q. agrifolia, and consumed more Q. agrifolia acorns than P. californicus. Relative to P. boylii, P. californicus was a habitat generalist that did not discriminate among canopy plants for nest sites and had a broad diet. At high densities of P. californicus, the 2 species were negatively numerically associated. Both interspecific interactions and habitat partitioning (canopy level), via the specialization of P. boylii on Q. agrifolia, appear to facilitate the coexistence of P. boylii and P. californicus.