  Solar wind is probably the best laboratory to study turbulence in
astrophysical plasmas. In addition to the presence of magnetic field, the
differences with neutral fluid isotropic turbulence are: weakness of
collisional dissipation and presence of several characteristic space and time
scales. In this paper we discuss observational properties of solar wind
turbulence in a large range from the MHD to the electron scales. At MHD scales,
within the inertial range, turbulence cascade of magnetic fluctuations develops
mostly in the plane perpendicular to the mean field. Solar wind turbulence is
compressible in nature. The spectrum of velocity fluctuations do not follow
magnetic field one. Probability distribution functions of different plasma
parameters are not Gaussian, indicating presence of intermittency. At the
moment there is no global model taking into account all these observed
properties of the inertial range. At ion scales, turbulent spectra have a
break, compressibility increases and the density fluctuation spectrum has a
local flattening. Around ion scales, magnetic spectra are variable and ion
instabilities occur as a function of the local plasma parameters. Between ion
and electron scales, a small scale turbulent cascade seems to be established.
Approaching electron scales, the fluctuations are no more self-similar: an
exponential cut-off is usually observed indicating an onset of dissipation. The
nature of the small scale cascade and a possible dissipation mechanism are
still under debate.
