Connecting flights do not always automatically transfer your luggage, and the rules depend heavily on whether you are on a "through-ticket" (a single booking) and the countries involved in your journey. If you have a domestic-to-domestic layover in the United States on a single ticket (e.g., San Francisco to Denver to New York), the airline's ground crew will typically transfer your bags between aircraft, and you will not see them until you reach your final destination. However, if you are arriving on an international flight into the U.S., you are legally required to collect your bags at your first "port of entry" to clear customs, even if your bags are tagged to your final destination. You then immediately place them on a "re-check" belt after exiting the customs area. For international-to-international transfers in major hubs like Dubai or Singapore, the bags are almost always transferred automatically without your intervention. If you have booked two "separate tickets" (a self-transfer), you will always have to collect your bags at the layover city and check them in again for the second flight, which involves clearing security and potentially needing a transit visa.