This paper begins with a discussion of the meaning and importance of error analysis in language teaching and learning. The practical implications of what error analysis is for the classroom teacher are discussed, along with several possible systems for classifying learner errors. The need for the language teacher to establish certain priorities in error correction, since some errors are more detrimental to effective communication than others, is stressed. Brief guidelines are given on how a teacher might begin to collect data to study the kinds of errors made by his or her students. (PMP)