  In the last decade it has been proven that the standard spin wave theory was
able to provide accurate zero-temperature results for a number of
low-dimensional Heisenberg spin systems. In this chapter we introduce the main
ingredients of the spin-wave technique using as a working model the two-leg
mixed-spin ferrimagnetic ladder and the Dyson--Maleev boson formalism up to
second order in the spin-wave interaction. In the remainder, we survey typical
applications in low-space dimensionality as well as some recent modifications
of the theory admitting a quantitative analysis in magnetically disordered
phases. The presented spin-wave results are compared with available numerical
estimates.
