This article presents the subject of English for Specific (or Special) Purposes (ESP) from the point of view of the school teacher or university lecturer attempting to teach science to students for whom the medium of instruction is a second language. The skills a student needs in order to achieve success in a science are analyzed as: (1) discipline-specific--strategies for extracting and patterning the data in a particular field, (2) general organizational--for presenting data in written and iconic form, and (2) linguistic skills. In a second-language situation, the teacher cannot assume that students come equipped with these skills; he must, therefore, teach them in addition to the scientific content of the course. This places constraints on the organization of the course and on the materials that can be used successfully. High-level science materials, such as lectures and lesson notes, modifiable to fit the level of the students' abilities. What seems to be called for is a set of integrated materials which require increasingly complex communication skills and which provide for individualized learning activities. The close cooperation of science and language specialists is needed to produce such materials in many scientific areas. (TL)