  Recent improvements in instrumentation have established resonant inelastic
x-ray scattering (RIXS) as a valuable new probe of the magnetic excitations in
the cuprates. This article introduces RIXS, focusing on the Cu $L_3$ resonance,
and reviews recent experiments using this technique. These are discussed in
light of other experimental probes such as inelastic neutron scattering and
Raman scattering. The success of these studies has motivated the development of
several new RIXS spectrometers at synchrotrons around the world that promise,
among other improvements, 5-10 times better energy resolution. We finish by
outlining several key areas which hold promise for further important
discoveries in this emerging field.
