In this chapter, we select some materials for further study. In Section 5.1, an SEIR model for measles is presented and analyzed. This is an example of higher dimensional models, models having more than two modeling equations. For the local stability analysis, we demonstrate how the Routh–Hurwitz conditions can be used to show that the eigenvalues of a \(3\times 3\) matrix have negative real parts. The proof of global stability of the endemic equilibrium using a Lyapunov function is adapted from the work of Korobenikov and Maini  (Math Biosci Eng 3(4226):79–82).