Delineating delirium phenomenology facilitates detection, understanding neuroanatomical endophenotypes, and patient management. This compendium reflects an integrated research plan executed over a five year period, employing detailed, standardized phenomenological assessments cross-sectionally and longitudinally. Motor activity studies were controlled and included both subjective and objective measures, aimed at identifying a new approach to defining this clinical subtype as a more pure motor disturbance. This work confirms delirium as a complex neuropsychiatric disorder involving widespread dysfunction of higher cortical centres that includes core disturbances of cognition, higher level thinking and circadian rhythms. Although delirium is characterised as a unitary syndrome, not all symptoms follow the same trajectory over the course of an episode; non-cognitive symptoms are more fluctuating. Attention is characteristically disproportionately impaired, relatively less fluctuating, and a key indicator of delirium. Longer delirium episodes involve more prominence of cognitive symptoms. Delirium symptoms overshadow dementia symptoms whether or not these conditions co-occur. Impaired forward spatial span is especially discriminating between delirium and dementia. Motor activity disturbances are almost invariable in delirium and can distinguish clinical subtypes that are relatively stable over the course of an episode. These motor-defined subtypes have similar cognitive impairment severity but differ for noncognitive symptom expression and prognosis.