The idiopathic inflammatory myopathies (IIMs) represent a heterogeneous group of disorders characterized by mononuclear cell infiltration of muscle and varying degrees of muscle dysfunction. To better understand the pathogenesis of these diseases, investigators have devised a number of infectious, genetic, and antigen-induced animal models that replicate different aspects of muscle involvement. Although the underlying heterogeneity of disorders encompassed by IIM precludes development of a single unifying model, several recently developed experimental systems have provided tremendous insight regarding the contributions of both immune- and non–immune-mediated disease pathways in various subsets of IIM. In turn, by elucidating the pathogenic roles of such disparate factors as endoplasmic reticulum stress and innate immune signaling, these models have established the foundation for more novel, targeted therapeutic intervention.