Organic thermally activated delayed fluorescence (TADF) materials have been widely explored as emitters in OLEDs over the past decade because of their ability to harvest both triplet and singlet excitons to produce light, leading to OLEDs with TADF emitters that can achieve 100% internal quantum efficiency (IQE). Multi-resonant TADF emitters, a sub-class of TADF materials, show characteristically narrowband emission and high FPL due to their rigid structures and their possessing an emissive S1 state of short-range charge transfer (SRCT) character. Since the first reported example of a MR-TADF emitter by Hatakeyama and co-workers in 2016, now more than 250 examples of MR-TADF emitters for OLEDs have been reported, with many examples of devices showing maximum external quantum efficiencies (EQEmax) of >30%. Of the reported MR-TADF emitters there are a small number that are chiral and CPLactive.