  A leap forward has been performed due to the space-borne missions, MOST,
CoRoT and Kepler. They provided a wealth of observational data, and more
precisely oscillation spectra, which have been (and are still) exploited to
infer the internal structure of stars. While an adiabatic approach is often
sufficient to get information on the stellar equilibrium structures it is not
sufficient to get a full understanding of the physics of the oscillation.
Indeed, it does not permit one to answer some fundamental questions about the
oscillations, such as: What are the physical mechanisms responsible for the
pulsations inside stars? What determines the amplitudes? To what extent the
adiabatic approximation is valid? All these questions can only be addressed by
considering the energy exchanges between the oscillations and the surrounding
medium.
  This lecture therefore aims at considering the energetical aspects of stellar
pulsations with particular emphasis on the driving and damping mechanisms. To
this end, the full non-adiabatic equations are introduced and thoroughly
discussed. Two types of pulsation are distinguished, namely the self-excited
oscillations that result from an instability and the solar-like oscillations
that result from a balance between driving and damping by turbulent convection.
For each type, the main physical principles are presented and illustrated using
recent observations obtained with the ultra-high precision photometry
space-borne missions (MOST, CoRoT and Kepler). Finally, we consider in detail
the physics of scaling relations, which relates the seismic global indices with
the global stellar parameters and gave birth to the development of statistical
(or ensemble) asteroseismology. Indeed, several of these relations rely on the
same cause: the physics of non-adiabatic oscillations.
