All surgeons within teaching hospitals share in the collective responsibility for training more junior doctors. A large proportion of training focuses around developing good clinical practice and ensuring the trainee is reaching competency. Formal structured teaching sessions aim to improve the trainee's theoretical knowledge and wider understanding. But surgical trainees must also learn how to operate. In order to do this, a more experienced surgeon must teach and supervise them in how to perform common procedures. This article discusses effective teaching within the operating theater, drawing on the author's own reflective practice. It introduces the concepts of theater prerequisites, used for assessing the suitability of theater cases for teaching, and active observation as one of the methodologies for teaching in theater.