The focus of the present study is the use of communication strategies in teacher talk in ESL/EFL classrooms. Communication strategies consist of adjustments made by speakers to the formulation of their talk in order to facilitate communication, and these are clearly a potentially important aspect of teacher talk. The study uses a mixed method design to investigate firstly the type and frequency of communication strategies and their patterns of relationship across teachers grouped in terms of language background and teaching institution; and secondly the type and frequency of strategy use in relation to the focus of talk across the different phases of a standard lesson. The participants were three native speaker and six non-native speaker teachers, across three different ESL/EFL instructional settings. The data consist of a total of twenty seven recordings, made up of three lessons with each teacher. The detailed examination of the database revealed that the participant teachers used both conversational modifications and lexical-compensatory strategies in their talk with students. The quantitative analysis showed that the two types of strategy occurred with different frequencies. No important differences were found between NS and NNS teachers. However, significant task-related differences were detected. Finally, a case study of three teachers revealed a relationship between the focus of talk and the incidence of communication strategies across the phases of the analysed lesson. The implications of these results are firstly that communication strategies are indeed a central element of teacher talk; secondly, that lexical-compensatory strategies and meaning negotiation strategies both contribute significantly to the construct; thirdly, that their use is important for both native speaker and non-native speaker teachers; fourthly, that they are used with significantly different frequencies and functions; and finally, that their use is influenced by teaching focus and activity type.