This booklet begins by examining the role played by evaluation in course and curriculum development, and then shows how the basic "error elimination" approach advocated by the philosopher Karl Popper can be used as a basis for the on-going evaluation of instructional systems. Next, two contrasting paradigms of evaluation are described, one that concentrates on measuring the outcomes of the instructional system (the agricultural/botanical or scientific approach) and one that pays more attention to what happens during the educational process itself (the social/anthropological or illuminative approach). Finally, five diagnostic techniques commonly used as part of an evaluation strategy are reviewed and the respective uses, strengths, and weaknesses of each are discussed: (1) results from student assessment; (2) student questionnaires and interviews; (3) observation of the instructional system in progress; (4) feedback from teaching staff directly involved with the instructional system; and (5) feedback from people having an indirect link with the instructional system. Models of the systems approach to course development, the role of an instructional system, and the general methodological approach advocated by Popper are provided, as well as extracts from a Likert scale and a semantic differential scale taken from course evaluation questionnaires. An annotated list of three items recommended for further reading is included. (MES)