You can sue an airline for lost luggage, but it is usually considered a last resort after exhausting the airline's internal claims process. Under the Montreal Convention for international flights and DOT regulations for U.S. domestic flights, airlines are legally required to compensate you for lost, damaged, or delayed baggage up to specific liability limits (currently around $3,800 for domestic and approx. $1,700 for international). A bag is officially considered "lost" if it hasn't arrived within 21 days. Before suing, you must file a Property Irregularity Report (PIR) at the airport and a formal written claim within specified windows (7 days for damage, 21 days for delay). If the airline denies a valid claim or offers an unfairly low settlement, you can take them to small claims court, which is often the most cost-effective legal route. However, most passengers find that travel insurance or credit card protections provide faster reimbursement than a lawsuit. Be aware that the "fine print" in your ticket contract often excludes liability for high-value items like jewelry or electronics, so you would need to prove gross negligence to recover more than the standard liability cap.