Unintentional weight loss in people older than 65 years is associated with increased morbidity and mortality. Nonmalignant diseases are more common causes of unintentional weight loss in this population than malignant causes. However, malignancy accounts for up to one-third of cases of unintentional weight loss. Medication use and polypharmacy can interfere with the sense of taste or induce nausea and should not be overlooked as causative factors. Social factors such as isolation and financial constraints may contribute to unintentional weight loss. A readily identifiable cause is not found for 6% to 28% of cases. Recommended tests include age-appropriate cancer screenings, complete blood count, basic metabolic panel, liver function tests, thyroid function tests, C-reactive protein level, erythrocyte sedimentation rate, lactate dehydrogenase measurement, ferritin, protein electrophoresis, and urinalysis. Chest radiography and fecal occult blood testing should be performed. Further imaging and invasive testing may be considered based on initial evaluation. When the initial evaluation is unremarkable, a three- to six-month observation period is recommended with follow-up based on clinician and patient preferences. Treatment should focus on the underlying cause if known. Dietary modifications that consider patient preferences and chewing or swallowing disabilities should be considered. Appetite stimulants and high-calorie supplements are not recommended. Treatment should focus on feeding assistance, addressing contributing medications, providing appealing foods, and social support.