The linear-regression ideas are building blocks for many other statistical models. The R project’s archive (CRAN, http://cran.r-project.org/) warehouses over 300 add-on packages to R, many of which implement extensions to the linear-regression model covered in the last two chapters. In this chapter, we look at two extensions: logisticregression models and nonlinear models. Our goal is to illustrate that most of the techniques used for linear models carry over to these (and other) models.