We consider infinite-horizon economies populated by a continuum of agents subject to idiosyncratic shocks. This framework contains models of saving and capital accumulation with incomplete markets in the spirit of works by Bewley, Aiyagari, and Huggett; models of entry, exit, and industry dynamics in the spirit of Hopenhayn’s work; and dynamic models of occupational choice and search models as special cases. Robust and easy-to-apply comparative statics results are established with respect to exogenous parameters as well as various kinds of changes in the Markov processes governing the law of motion of the idiosyncratic shocks.