Hallucinations are one of the most interesting and least understood of all human experiences. This commentary addresses the ideas which most influenced my thinking in the past 20 years and what I believe to be the most currently promising area of enquiry. Interest in hallucinations reaches far back into antiquity and across cultures. The similarity of hallucinations in mental illness with the perceptual experiences reported by individuals who not mentally unwell has long been recognized. Early scientific research on hallucinogen drugs such as lysergic acid diethylamide (LSD) was criticized and then withdrawn, but its recent revival offers new opportunities to examine the mechanism and ‘process’ of hallucinating. Many psychedelic compounds can elicit intense and realistic hallucinations. The study of hallucinogens conducted in carefully controlled and supervised settings and with individuals who are not mentally unwell opens exciting new possibilities. For example, it may be possible to study the temporal shifts in perceptual awareness, decode what influences the contents, affect, meaning, and appraisals of hallucinations and guide novel psychotherapy techniques and drug therapy.