Two-way analysis of variance (ANOVA) is a statistical technique used to analyze data from a study in which a researcher wishes to examine both the separate and the combined effects of two categorical independent variables, called factors, on a continuous dependent (or outcome) variable. While the ideas of ANOVA as a statistical approach date back more than two centuries, it was not until the seminal work of R. A. Fisher in the 1920s on analyzing data from complex experiments that two-way ANOVA became a popular, reliable procedure used by practitioners and methodologists alike. This entry first describes the data analytic context for ANOVA and the logic behind its implementation. Two-way ANOVA is then introduced and several key analytic elements are discussed in the context of ...