Study of the luminescence of Rare Earth ions introduced into III-nitride semiconductor hosts produces a wealth of important information. This chapter describes investigations of photoluminescence and cathodoluminescence spectroscopy on a range of RE-implanted samples, with hosts including GaN, AlGaN and AlInN. Raising the post-implantation annealing temperature is shown to lead to a dramatic increase in RE luminescence intensity, and methods to allow annealing well above the growth temperature of the host are discussed. The high-brightness samples that result enable the resolution of additional fine-structure in the luminescence from GaN:Eu and clarification of multiple sites for the RE. Measurements for AlGaN hosts covering the entire composition range point to the importance of core-excitons in the luminescence process. Adding in information from X-ray microanalysis and high spatial resolution luminescence mapping reveals further details of the effects resulting from annealing and of changes in host composition.