The optical spectroscopic properties of Cr³⁺ in LiNbO₃ have been investigated using optical absorption, fluorescence, fluorescence line narrowing (FLN), selective excitation and radiative lifetime measurements. The present results are compared with data obtained using other techniques including electron spin resonance (ESR) and electron nuclear double resonance (ENDOR), and shown to be consistent with there being five Cr³⁺ centres. The predominant centre is due to substitution at the Li⁺ site, which provides the weak crystal field in which Cr³⁺ ions emit into a broad ⁴T₂ to ⁴A₂ band. Using FLN, two centres experiencing a stronger crystal field are shown to be due to substitution at this same site, probably perturbed by the location of Nb⁵⁺ antisites and Nb⁵⁺ vacancies in the next-nearest-neighbour cation shell. The addition of Mg²⁺ ions to LiNbO₃ appears not to create new Cr³⁺ complexes: rather it modifies the nature of the disorder, thereby changing the relative concentrations of the different centres. To this extent it becomes possible to identify two other lightly occupied Cr³⁺ centres where substitution is at the Nb⁵⁺ site. This total of five Cr³⁺ centres in LiNbO₃ gives a consistent interpretation of all the available spectroscopic evidence, including ESR and ENDOR, while pointing to the difficulties of theoretical work in sites where the differences in the energy levels of Cr³⁺ ions are too small to be distinguished by the available models.