The standard Susceptible-Infected-Recovered (SIR) model is a compartmental model for the spread of an infectious disease through a host population. This project analyzes the standard SIR model, the SIR model without lifetime immunity, and the SIR model on a network of nodes to investigate conditions that create an epidemic. Techniques from the first two analyses, numerical simulation, and a small dive into parameter estimation are involved in analyzing the SIR model on a network.