This paper discusses the problem of how to deal effectively with students' errors from the perspective of Error Analysis. Basic aspects of the theory such as "interlanguage,""learning strategies" and "the interpretation of errors" are introduced; and empirical data from child language learning studies are presented to support the underlying assumptions that a language learner creates a tentative system of rules from the language data he is exposed to and that this system enables him to use the language. Because of the parallels between second language learning and first language acquisition, it is considered reasonable to extend these assumptions to adult second language learning. In light of this theory, errors are shown to be signs of learning rather than signs of failure. It is proposed that this calls for a switch in focus from the second language itself, to the learner of the second language. This implies that the teacher's role would be in studying the students' interlanguages and facilitating their development rather than in correcting their errors. The implications and some practical applications of this idea are discussed. (Author)