There is increasing consensus that form-focused instruction helps learners in communicative or content-based instruction to learn features of the target language that they may not acquire without guidance. The subject of this article is the role of instruction that is provided in separate (isolated) activities or within the context of communicative activities (integrated). Research suggests that both types of instruction can be beneficial, depending on the language feature to be learned, as well as characteristics of the learner and the learning conditions. For example, isolated lessons may be necessary to help learners who share the same first language (L1) overcome problems related to L1 influence on their interlanguage; integrated instruction may be best for helping learners develop the kind of fluency and automaticity that are needed for communication outside the classroom. The evidence suggests that teachers and students see the benefits of both types of instruction. Explanations for the effectiveness of each type of instruction are drawn from theoretical work in second language acquisition and cognitive psychology as well as from empirical research. (Contains 9 footnotes.)