This study of Old Spanish and present-day Mexico and New Mexico data develops a grammaticization account of variation in progressive constructions. Diachronic changes in cooccurrence patterns show that grammaticization involves reductive change driven by frequency increases. Formal reduction results in the emergence of auxilliary-plus-gerund sequences as fused units. Semantically, the constructions originate as spatial expressions; their grammaticization involves gradual loss of locative features of meaning. Semantic generalization among parallel evolutionary paths results in the competition among different constructions in the domain of progressive aspect. Patterns of synchronic variation follow from both the retention of meaning differences and the routinization of frequent collocations, as well as sociolinguistic factors. Register considerations turn out to be crucial in evaluating the effects of language contact. Purported changes in Spanish — English bilingual varieties are largely a feature of oral, informal language rather than a manifestation of convergence.