What do combustion engines, fusion reactors, weather forecast, ocean ?ows, our sun, and stellar explosions in outer space have in common? Of course, the physics and the length and time scales are vastly di?erent in all cases, but it is alsowellknownthatinallofthem, onsomerelevantlengthscales, thematerial ?ows that govern the dynamical and/or secular evolution of the systems are chaotic and often unpredictable: they are said to be turbulent. In fact, the term turbulence is used for an enormous variety of p- nomena in very di?erent ?elds, including geophysics, astrophysics, and - gineering....