This document summarizes key aspects of a second-order control system's time domain response. It defines a general second-order transfer function and explains that systems can be overdamped, underdamped, undamped, or critically damped depending on the damping ratio ζ. The natural frequency ωn and damping ratio ζ are described. For an underdamped second-order system with 0< ζ <1 and ωn > 0, the document examines the system's response to a unit step input, focusing on the transient and steady state responses. Poles are described as complex if ζ< 1 and the system is parameterized by ζ and ωn.