In Section 2.1, we introduce the ssr function for general smoothing spline regression models with one variable. In sections 2.2 to 2.4, we show how to use ssr to fit more complicated models such as partial spline models, smoothing spline ANOVA (SS ANOVA) models for correlated observations and/or observations with unequal variances, and SS ANOVA models for data from exponential families.