  Magnetic reconnection is a process that changes magnetic field topology in
highly conducting fluids. Traditionally, magnetic reconnection was associated
mostly with solar flares. In reality, the process must be ubiquitous as
astrophysical fluids are magnetized and motions of fluid elements necessarily
entail crossing of magnetic frozen in field lines and magnetic reconnection. We
consider magnetic reconnection in realistic 3D geometry in the presence of
turbulence. This turbulence in most astrophysical settings is of pre-existing
nature, but it also can be induced by magnetic reconnection itself. In this
situation turbulent magnetic field wandering opens up reconnection outflow
regions, making reconnection fast. We discuss Lazarian \& Vishniac (1999) model
of turbulent reconnection, its numerical and observational testings, as well as
its connection to the modern understanding of the Lagrangian properties of
turbulent fluids. We show that the predicted dependences of the reconnection
rates on the level of MHD turbulence make the generally accepted Goldreich \&
Sridhar (1995) model of turbulence self-consistent. Similarly, we argue that
the well-known Alfv\'en theorem on flux freezing is not valid for the turbulent
fluids and therefore magnetic fields diffuse within turbulent volumes.
  This is an element of magnetic field dynamics that was not accounted by
earlier theories. For instance, the theory of star formation that was
developing assuming that it is only the drift of neutrals that can violate the
otherwise perfect flux freezing, is affected and we discuss the consequences of
the turbulent diffusion of magnetic fields mediated by reconnection.
