Two studies examined individual cognitive differences affecting the acquisition of second language word forms. Experiment 1 measured 40 undergraduates' ability to learn phonological sequences, their phonological short-term store capacity as indexed by ability to repeat nonwordlike nonwords, and their learning of novel foreign language vocabulary (German) in an experimental task. Phonological sequence learning predicted receptive vocabulary learning. Phonological sequence learning and phonological store capacity made independent additive contributions to productive vocabulary learning. Experiment 2 determined the interactions of phonological sequence learning ability, phonological store capacity, and second language acquisition during a longitudinal field study of 44 novice undergraduate learners of Spanish during a 10-week course. Students' initial skill in phonological sequence learning predicted their final levels of Spanish receptive language and their eventual ability to repeat Spanish-wordlike nonwords. The results suggest that phonological store capacity and phonological sequence learning ability are initially separable constraints on second language vocabulary acquisition and that sequence learning ability underpins the acquisition of long-term phonological knowledge. Subsequent apprehension and consolidation of a novel word form is a product not only of phonological short-term store capacity but also of this long-term knowledge of the phonological regularities of language.