This paper is part of a series of applied statistics monographs intended to provide supplementary reading for applied statistics students. In the present paper, derivations of the unbiased standard error of estimate for both the raw score and standard score linear models are presented. The derivations for raw score linear models are presented in graduated steps of generality for one, two, three, and any finite number of predictors. A brief overview of regression analysis precedes the derivations. Appendices include: (1) errata for a derivation of the sample multiple correlation formula; and (2) a discussion of linear and nonlinear regression models. (LMO)