This document outlines the key topics in Chapter 5 of the textbook for the MCE 440 - Vibrations course taught by Eng. Omar Al-Ostah. The chapter discusses 2 degree of freedom (DOF) systems, including: 1) Developing the equations of motion for a 2 DOF spring-mass-damper system using Newton's second law applied to each mass. 2) Expressing the equations of motion in matrix form using the mass, damping, and stiffness matrices. 3) Analyzing the frequency response and complex frequency response of a damped 2 DOF system under harmonic forcing. 4) Working through an example problem of a plate supporting a pump.