  Magnetic reconnection is a fundamental process in a plasma that facilitates
the release of energy stored in the magnetic field by permitting a change in
the magnetic topology. In this article we present a review of the current state
of understanding of magnetic reconnection. We discuss theoretical results
regarding the formation of current sheets in complex 3D magnetic fields, and
describe the fundamental differences between reconnection in two and three
dimensions. We go on to outline recent developments in modelling of
reconnection with kinetic theory, as well as in the MHD framework where a
number of new 3D reconnection regimes have been identified. We discuss evidence
from observations and simulations of solar system plasmas that support this
theory, and summarise some prominent locations in which this new reconnection
theory is relevant in astrophysical plasmas.
