  Two-dimensional turbulent flows, and to some extent, geophysical flows, are
systems with a large number of degrees of freedom, which, albeit fluctuating,
exhibit some degree of organization: coherent structures emerge spontaneously
at large scales. In this short course, we show how the principles of
equilibrium statistical mechanics apply to this problem and predict the
condensation of energy at large scales and allow for computing the resulting
coherent structures. We focus on the structure of the theory using the language
of large deviation theory.
