This paper investigates the relationship between working memory capacity and inhibitory control as a function of L2 proficiency. Students (n =121) in first and third year university Spanish classes were given L1 and L2 reading span tests and an L1 and L2 Stroop interference task. The two groups had significantly different L2, but not L1 working memory scores. The correlation between L1 and L2 working memory scores was significant for the 3rd year group, but not for the 1st year group. L2 proficiency did not affect inhibitory control. A model illustrating the interrelatedness of inhibition, proficiency and working memory capacity is proposed. Finally, we raise a methodological issue regarding the use of L2 working memory tests.