Sexual cannibalism, the consumption of the male by the female before, during, or after mating, can be a striking example of sexual conflict with potentially large fitness consequences for males and females. In this review, we examine how ecological and phylogenetic factors may affect the occurrence and frequency of sexual cannibalism within and among species. Ecological factors such as food and mate availability may primarily influence cannibalism by affecting the benefit of cannibalism for females. Phylogenetic factors such as feeding mode, sexual size dimorphism, certain mating behaviors, and genetic constraints may influence the vulnerability of the male to the female or the propensity of females to attack males. Although in some cases it may be difficult to separate the effects of co-occurring factors, in other cases comparative and phylogenetic approaches may aid in determining the influence of ecological and phylogenetic factors for the evolution of sexual cannibalism.