**Statistical mechanics of large scales in turbulent flows**

In many turbulent flows, scales larger than the forcing scale display

equipartition of energy. This familiar result of equilibrium statistical

physics could look surprising in turbulent flows which are considered as

a canonical example of an out of equilibrium dissipative system. After

displaying several examples and discussing this result, we show that

concepts from equilibrium statistical physics can also be used to

describe transitions between different turbulent regimes when a

governing parameter is varied. More precisely, the truncated Euler

equation provides a tool to describe the dynamics of large scales and

bifurcations that occur on a turbulent background. Finally, we show how

the dynamics of these large scale is related to 1/f type noise observed

in many turbulent flows and elsewhere.