The analysis of covariance as a procedure for statistical correction of the effects for an extraneous variable, called a "covariate," is presented. An heuristic data set is used to make the discussion of the calculation of ANCOVA partitions easier to follow. A discussion of homogeneity of regression as an essential condition to be met when conducting ANCOVA is discussed. Data reliability and the interpretation of the residualized dependent variable as major issues when applying ANCOVA are also discussed. It is suggested that caution must be exerted when applying ANCOVA to statistically correct for differences due to a covariate. Five tables and two appendixes. (Contains 24 references.) (Author)