Contraction of want to to wanna is subject to constraints that have been related to the operation of Universal Grammar. Contraction appears to be blocked when the trace of an extracted wh-word intervenes. Evidence for knowledge of these constraints by young English-speaking children has been taken to show the operation of Universal Grammar in early child language acquisition. The present study investigates knowledge of these constraints in adults, both English native speakers and advanced Korean learners of English. The results of three experiments — using elicited production, oral repair, and grammaticality judgments — confirmed native speaker knowledge of the constraints. A second process of phonological elision may also operate to produce wanna. Learners also showed some differentiation of contexts, but much less clearly than native speakers. We speculate that non-natives may be using rules of complement selection, rather than the constraints of Universal Grammar (UG) to control contraction.