Inherited microorganisms that manipulate the reproduction of their host are a common feature in arthropod biology. Although research initially concentrated on why these manipulations were observed, more recent study has emphasized the profound effects they may have on the ecology and evolution of their host. We review the natural history and evolutionary ecology of inherited reproductive parasites, before examining their impact on host ecology and evolution. We posit that sex-ratio distorting microorganisms sometimes dominate their host's microevolution and reproductive ecology, driving extremely rapid natural selection, altering the molecular evolution landscape, and potentially causing evolution in conserved systems such as sex determination. The evolutionary importance of symbionts inducing cytoplasmic incompatibility lies more in the barriers to gene flow they can produce, which may then contribute to reproductive isolation and speciation. Throughout, we link theory with empirical data, point to areas of ignorance, and identify promising avenues of future research.