Though the need for a language or languages to describe teacher behavior has been recognized for some time, few systems of analysis exist. A conceptual framework and a set of terms have been developed to describe the messages students and teachers send and receive in second language classrooms. This system is called FOCUS (an acronym for Foci for Observing Communications Used in Second language instruction). These charactersitics of messages are noted: the source, e. g., teacher or student; the medium used, e.g., speech, touch, etc.; how the medium is used; the content of the message; and the pedagogical purpose. Though designed as a research instrument to discover how teachers treat errors, what the distinctive features of different "schools" of language teaching are, and which characteristics of messages are most frequent and which least frequent in language classes at different levels taught by teachers with different amounts of training, the instrument has a number of practical uses. Observation guides can be made by extracting categories from FOCUS. These guides can be used as observation checklists to analyze tests and materials, the growth of teachers in teacher education programs, and the extent to which teachers meet competencies that are listed in performance based teacher education programs; finally, the guides can be used as tools in training teachers how to teach second languages. (Author/AM)