In this paper the concept of “lexical unit” as proposed by Cruse (1986) isintroduced in the context of L2 vocabulary learning to replace the rather vague notion of“word.” In the first part of the paper, this concept is defined in terms of lexicalsemantics and then applied to the L2 learning task. The second part describes two experimentalstudies in which the learning of different types of lexical units is examined. In the first study,totally new lexical units are compared with multiword items that are made up of familiar forms. Inthe second experiment, different types of new senses of familiar forms are compared. Both studiesunderscore the importance of knowledge of form—but not of previously learnedmeaning—for the learning of new meanings for familiar forms.