Examples are an excellent tool for introducing technical topics such as regression. However, this chapter has also used algebra as well as basic probability and statistics to give you further insights into regression analysis. Going forward, we will be studying multivariate relationships. With many things happening concurrently in several dimensions, algebra is no longer useful for providing insights. Instead, we will need matrix algebra. This supplement provides a brief introduction to matrix algebra to allow you to study the linear regression chapters of this text. It re-introduces basic linear regression to give you a feel for things that will be coming up in subsequent chapters when we extend basic linear regression to the multivariate case. Appendix A3 defines additional matrix concepts.