Mimicry rings are communities of mimetic organisms that are excellent models for ecological and evolutionary studies because the community composition, the nature of the species interactions, the phenotypes under selection, and the selective agents are well characterized. Here, we review how regional and ecological filtering, density- and frequency-dependent selection, toxicity of prey, and age of mimicry rings shape their assembly. We synthesize findings from theoretical and empirical studies to generate the following hypotheses: (a) the degree of unpalatability and age of mimicry rings increase mimicry ring size and (b) the degree of unpalatability, generalization of the aposematic signal, and availability of alternative prey are positively related to the breadth of the protection umbrella for an aposematic signal and negatively related to the degree of mimetic resemblance. We also provide a phylogenetic framework in which key aspects of mimicry ring diversification may be studied.