 Since the 1930s, researchers have been investigating the quantum theory of the damped harmonic oscillator by including a reservoir to deal with energy dissipation, but a discrete reservoir cannot directly yield ohmic damping dynamics. Continuous oscillators as a reservoir are used to quantize the harmonic oscillator with ohmic damping and general damping behavior, and the dynamics of a damped oscillator is determined by an arbitrary effective susceptibility that follows Kramer-Skronig relations. This approach provides an alternative description of nanomechanical and optomechanical systems. This article was offered by T. G. Philbin.