The purpose of this training workbook is to provide the user with an understanding of Analysis of Covariance (ANCOVA) sufficient to allow him to identify situations in which it can increase the credibility and the statistical power of the analysis. The module provides a conceptual, nonmathematical overview of the purposes of ANCOVA. The assumptions underlying the use of ANCOVA and the consequences of their violation are summarized. An illustrative ANCOVA problem is employed to graphically illustrate how ANCOVA removes bias and increases statistical power. A self-instructional problem set is included as illustration and reinforcement for the learner. The module concludes with a mastery test. The workbook is designed for students in intermediate statistics and experimental design courses and for research and evaluation personnel, especially those being trained on the job. The book requires familiarity with simple regression and one-factor analysis of variance. (Author/SE)