A theory for the transmission dynamics and control of malaria was developed around a set of concepts, quantities, and mathematical models introduced by Ronald Ross. Decades later, Macdonald linked Ross's models to epidemiological and entomological data, developed the concept of the basic reproductive number, R0, and proposed a rudimentary theory of control based on sensitivity to parameters. Here, we review development of the Ross–Macdonald model, present one simple version, and provide an eclectic critique of the theory based on studies conducted more recently. While mosquito populations are logically necessary for mosquito-borne pathogen transmission, the study of transmission since then shows it is noisy, heterogeneous, and complex. Heterogeneity, stochasticity, and complexity represent important challenges for applying theory in context.