The three main subspecies of house mice, Mus musculus castaneus, Mus musculus domesticus , and Mus musculus musculus, are estimated to have diverged ~325-500KYA. Resolution of the details of their evolutionary history is complicated by their relatively recent divergence, ongoing gene flow among the subspecies, and complex demographic histories. Previous studies have been limited to some extent by the number of loci surveyed and/or by the scope of the method used. Here we apply a method (IMa3) that provides an estimate of a population phylogeny while allowing for complex histories of gene exchange. Results strongly support a topology with M. m. domesticus as sister to M. m. castaneus and M. m. musculus . In addition, we find significant evidence of reciprocal gene flow between all pairs of subspecies. Our estimates of another key set of parameters, effective population size ( N e ), support previous results that the N e of M. m. castaneus is larger than that of the other two subspecies.