Exploratory factor analysis (EFA) is a multivariate statistical technique that is commonly used in language assessment research. It examines the interrelationships among variables, groups the variables into a smaller number of factors, and establishes their underlying structure, thereby providing evidence of construct validity and theory refinement. As a data reduction method, EFA is often used in questionnaire and test development to identify theoretical constructs, to examine if the designed items measure what they are supposed to measure, and to help revise and improve instruments. This chapter provides an introduction to conducting EFA with real data from an empirical example in the field of language assessment. A five-step procedure of conducting EFA is introduced, followed by a brief review of the literature on the studies that apply EFA in language assessment. Finally, an illustration of how to conduct EFA with real data is provided.