The paper reviews the coupling of mechanical and optical degrees of freedom via radiation pressure, focusing on the consequences of back-action in whispering-gallery dielectric micro-cavities. It presents a unified treatment of two key manifestations: parametric instability (parametric amplification) and radiation pressure back-action cooling. The parametric instability offers a novel "photonic clock" driven by light pressure, while radiation pressure cooling can surpass existing cryogenic technologies, providing cooling to phonon occupancies below unity and paving the way for cavity Quantum Optomechanics. The theoretical framework is developed using coupled mode equations, which describe the dynamics of the optical field and mechanical coordinate. The paper discusses the static and dynamic manifestations of radiation pressure forces, including mirror bistability and the creation of stokes and anti-stokes sidebands. Experimental results from microroid resonators are presented to verify the theoretical predictions, showing the effects of dynamic back-action on mechanical damping and amplification. The paper also explores the high spectral selectivity of cooling and amplification, allowing for targeted control of specific mechanical modes. Finally, it highlights the potential applications of these findings in metrology and quantum technology.The paper reviews the coupling of mechanical and optical degrees of freedom via radiation pressure, focusing on the consequences of back-action in whispering-gallery dielectric micro-cavities. It presents a unified treatment of two key manifestations: parametric instability (parametric amplification) and radiation pressure back-action cooling. The parametric instability offers a novel "photonic clock" driven by light pressure, while radiation pressure cooling can surpass existing cryogenic technologies, providing cooling to phonon occupancies below unity and paving the way for cavity Quantum Optomechanics. The theoretical framework is developed using coupled mode equations, which describe the dynamics of the optical field and mechanical coordinate. The paper discusses the static and dynamic manifestations of radiation pressure forces, including mirror bistability and the creation of stokes and anti-stokes sidebands. Experimental results from microroid resonators are presented to verify the theoretical predictions, showing the effects of dynamic back-action on mechanical damping and amplification. The paper also explores the high spectral selectivity of cooling and amplification, allowing for targeted control of specific mechanical modes. Finally, it highlights the potential applications of these findings in metrology and quantum technology.