In continuing this three-part review on validation of EEG-neurofeedback for optimal performance evi-dence is first provided for feedback influences on the CNS, the integration of EEG with fMRI methodologyas well as anatomical correlates. Then whereas Parts I and II reviewed the considerable behaviouraloutcome gains and evidence for their feedback causation, part III lays bare the not inconsiderable method-ological and theoretical conundrums. Cardinal assumptions amongst practitioners about specificity oftopography, behavioural outcome and frequency bands are critically examined. The hitherto mostlyneglected nature of feedback learning is reviewed including evidence of within- and between-sessionand successive baseline learning; the enduring impact on the tonic EEG; implications for experimentaldesign, individual differences and the trainer–participant interface; distinguishing between the learningand mastery of self-regulation; connectivity, ratio, unidirectional and multimodal feedback protocols.A thorough grounding in human neuroscience plus interpersonal skills are considered prerequisites forscientific advancement and ethically sound practice.