Aging involves progressive cellular senescence, telomere shortening, reduced mitochondrial efficiency, and accumulation of oxidative damage that collectively diminish organ reserve and adaptive capacity. Age-related changes include decreased glomerular filtration rate (affecting drug clearance), reduced hepatic first-pass metabolism (increasing drug bioavailability), diminished baroreceptor sensitivity (increasing orthostatic hypotension risk), decreased bone density from osteoclast-osteoblast imbalance, and reduced lean muscle mass (sarcopenia) that increases fall risk and functional decline. Delirium in hospitalized older adults results from a complex interplay of predisposing factors (cognitive impairment, sensory deficits, polypharmacy) and precipitating factors (infection, medications, metabolic disturbances, immobility) that disrupt cholinergic neurotransmission and cerebral metabolism. The geriatric RN conducts comprehensive geriatric assessment including cognitive screening, functional status evaluation, fall risk assessment, polypharmacy review using Beers criteria, and elder abuse screening to prevent iatrogenic harm and optimize outcomes.