This chapter introduces exploratory and confirmatory factor analysis (EFA and CFA) with brief mention of the closely related procedures principle components analysis and multidimensional item response theory. For EFA, emphasis is on rotation, the principle factors criterion, and methods for selecting the number of factors. CFA topics include identification, estimation of model parameters, and evaluation of model fit. EFA and CFA are introduced for continuous variables, and then extensions are described for non-normal continuous variables, and categorical variables. Study characteristics that influence sample size (for EFA or CFA) are discussed, and example analyses are provided which illustrate the use of three popular software programs.