A discussion of the use of thematic modules in content-based second language instruction argues that the approach has a number of advantages over others. Thematic modules are defined as longer than lessons and shorter than a course, and it is suggested that in a content-based approach, the module constitutes the basic unit of study. Content-based modules are seen as useful for: experimenting with minimal changes in existing courses; focusing more intensively on process-methodologies; adapting instruction to communicative performance testing methods; and packaging coursework for specialized vocabulary, as in English for Special Purposes (ESP). Students appear to like content-based language learning modules, and the method allows for considerable instructional flexibility. Modules, which can be either general or context-specific, are comprised of specific elements, including: starters, motivators, or probes to establish what schema learners bring to the topic and possible directions; a minimum of two inputs; treatment(s); synthesis; output task; and evaluation. Other common elements can be incorporated, including brainstorming, language focus, learner awareness training, independent investigation, and critical analysis. ESP modules contain many of the same design characteristics as general modules, but with input and output phases reflecting the area of specialization. (MSE)