Functional assessment systematically evaluates a patient's ability to perform activities necessary for independent living using validated tools that quantify functional capacity. The Katz Index of Independence in Activities of Daily Living assesses six basic ADLs (bathing, dressing, toileting, transferring, continence, feeding) on a dichotomous scale (independent vs. dependent), while the Lawton Instrumental Activities of Daily Living Scale evaluates eight more complex functions (telephone use, shopping, food preparation, housekeeping, laundry, transportation, medication management, financial management) that require higher cognitive and physical abilities. The Barthel Index provides a more granular scoring of 10 ADL domains with a 0-100 point scale that better detects incremental changes in functional status. Functional decline during hospitalization occurs in 30-60% of older adults due to immobility, sleep deprivation, malnutrition, polypharmacy, and loss of autonomy. The nurse performs baseline functional assessment on admission, reassesses with each significant clinical change, implements mobility programs to prevent hospital-acquired functional decline, collaborates with physiotherapy and occupational therapy, and uses functional assessment data to guide discharge planning, home care referrals, and family education about realistic expectations and support needs.