Introduction It is not at all self-evident that the experimental method as practised, for example, in the psychology laboratory or in psycholinguistic research is at all relevant for the conduct of research in language education, whether by teacher researchers or anybody else. There are several reasons for this, but there are also reasons to consider the experimental paradigm and some relevant examples to see what utility it might have. This chapter will concentrate first on the positive benefits of the experimental paradigm and later on some of the problems it poses for research on language learning inside and outside of classrooms, and for the teacher researcher who is the probable user of this book. It will not attempt to give a detailed step-by-step guide to experimental design, since there are many texts which discuss such matters to whatever degree of sophistication is required (Brown, 1988; Hatch and Farhady, 1982; Guilford and Fruchter, 1973); but it will discuss several of the most important principles, review the arguments about establishment of causality from Chapter 3, discuss features of design such as controls and counterbalances, and briefly analyse some published examples of experiments on classroom learning issues.