Success in learning a second or a foreign language, unlike success in first language acquisition, is very variable. Learner strategies, as conscious actions in learning and using a second or a foreign language, are one of the variable factors that have profound effects on how individual learners approach language learning and how successful they are. The more we learn about learner strategies, the more we gain a sense of the complex system of language learning and teaching. This paper critically reviews previous research on learner strategies and the implications of learner strategies for language teaching will be addressed. It aims to give some ideas to language teachers or administrators of how to: (1) explicitly involve learner strategies in a language curriculum, (2) provide language learners with a menu of the strategies that they can choose and adapt to different language learning tasks, and (3) create habits of good language learners.