  We discuss how the optomechanical coupling provided by radiation pressure can
be used to cool macroscopic collective degrees of freedom, as vibrational modes
of movable mirrors. Cooling is achieved using a phase-sensitive feedback-loop
which effectively overdamps the mirrors motion without increasing the thermal
noise. Feedback results able to bring macroscopic objects down to the quantum
limit. In particular, it is possible to achieve squeezing and entanglement.
