This article discusses applications of Second Language Acquisition (SLA) research to the preparation of language coursebooks. The author suggests a number of ways in which SLA research findings can help improve coursebooks and thereby enhance the learning of large numbers of students. Research leads us to consider learners as genuine speakers of the L2, as bilinguals who still have an L1 present in their minds and who do not all go about learning the L2 in the same way. Few coursebooks take into account these and other findings of SLA research, for example: that the acquisition of basic syntax precedes the acquisition of inflectional morphology, that most of the syntax to be learned is really part of the lexicon, or that vocabulary needs to be encountered in a structural and semantic context in order to be effectively acquired. Coursebook authors also need to bear in mind that pronunciation is necessary not only for communication but also for the actual learning of L2 forms, and that some aspects of the L2 writing system need to be explicitly taught. The author provides two sample lessons to illustrate how these research findings might be applied to the writing of a coursebook.