Quasi-periodic oscillations (QPOs) in compact astrophysical objects present a crucial window into the fundamental physics of very high-gravity environments. The present chapter proposes a comprehensive model that interprets QPOs across different frequency range from millihertz to kilohertz in different compact objects. Our model connects the observed QPO frequencies to the non-linear resonance of fundamental modes within the accretion disks, influenced by the central object’s spin. This model specifically explains the high-frequency QPOs in black holes and neutron stars and suggests that the same underlying physics is present behind the generation of lower-frequency QPOs. Additionally, the model extends to make predictions about the spins, masses, and radii of these compact objects based on the properties of the observed QPOs.