In this chapter, we focus on the conceptual and methodological issues involved in the analysis of more than two variables (that is, multivariate analysis). The analysis of more than two variables serves three major functions in empirical research: control, elaboration, and prediction. The first function, control, substitutes for the mechanism of experimental control when it is lacking. The second function, elaboration, clarifies bivariate relationships by introducing additional variables that help to explain bivariate associations. The third function, prediction, is served by the use of statistical procedures used when analyzing two or more independent variables to account for the variation in the dependent variable. This chapter discusses ways in which a third variable may enter into empirical research.