  The current theoretical and experimental situations are reviewed for
low-dimensional insulating systems with a low magnetic transition temperature
TM and pronounced short-range magnetic order above this temperature. Both the
standard and self-consistent spin-wave theories are shown to be insufficient to
quantitatively describe the experimental data on these systems.
Field-theoretical approaches taking into account the contribution of the
spin-fluctuation excitations (neglected in the spin-wave theories) to the
thermodynamic properties of ferro- and antiferromagnets are discussed.
