In this paper we test the hypothesis that an intensification of maize production preceded the development of a regional Moche political economy in the Moche Valley of north coastal Peru during the Early Intermediate period (400 B.C.—A.D. 600). To do so we analyze stable isotopic signatures of 48 bone apatite and 17 tooth enamel samples from human remains recovered from the site of Cerro Oreja, a large urban and ceremonial center in the Moche Valley. These remains date to the Guañape, Salinar, or Gallinazo phases and provide a diachronic picture of subsistence before the appearance of the Southern Moche state. The most notable patterns identified in the study include a lack of significant change in δ13 Capatite values from the Guañape to Satinar phases, followed by a significant enrichment in δ13 Capatite values from the Salinar to Gallinazo phases. Several lines of evidence, including archaeological context, dental data, and comparative carbon stable isotope data from experimental animal studies and studies of archaeological human remains support the interpretation that the observed 13C enrichment in stable isotope values in the Gallinazo phase primarily reflects maize intensification. The stable isotope data from Cerro Oreja thus suggest that a shift in subsistence toward a highly productive and storable crop may have served as an important precursor to state development during the Early Intermediate period in the Moche Valley.