  The current theoretical and experimental situation is reviewed for
low-dimensional (layered and chain-like) insulating systems. Such systems
possess a low magnetic transition temperature $T_M$ 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. Analytical expressions for $T_M$ and
temperature dependences of long-range order paramenters are obtained, which are
in a fair agreement with experimental data.
