This book provides an overview of solar wind turbulence from both the theoretical and
observational perspective. It argues that the interplanetary medium offers the best opportunity
to directly study turbulent fluctuations in collisionless plasmas. In fact during expansion
the solar wind evolves towards a state characterized by large-amplitude fluctuations in all
observed parameters which resembles at least at large scales the well-known hydrodynamic
turbulence. This text starts with historical references to past observations and experiments on
turbulent flows. It then introduces the Navier-Stokes equations for a magnetized plasma whose
low-frequency turbulence evolution is described within the framework of the MHD approximation.
It also considers the scaling of plasma and magnetic field fluctuations and the study of
nonlinear energy cascades within the same framework. It reports observations of turbulence in
the ecliptic and at high latitude treating Alfvénic and compressive fluctuations separately in
order to explain the transport of mass momentum and energy during the expansion. Further
existing models are compared with direct observations in the heliosphere. The problem of
self-similar and anomalous fluctuations in the solar wind is then addressed using tools
provided by dynamical system theory and discussed on the basis of available models and
observations. The book highlights observations of Yaglom's law in solar wind turbulence which
is one of the most important findings in fully developed turbulence and directly related to the
long-lasting and still unsolved problem of solar wind plasma heating. Lastly it includes a
short chapter dedicated to the kinetic range of fluctuations which has recently been receiving
more attention from the space plasma community since this is inherently related to turbulent
energy dissipation and consequent plasma heating. It particularly focuses on the nature and
role of the fluctuations populating this frequency range and discusses several model
predictions and recent observational findings in this context.
