Generally, you do not need to check in again for a connecting flight if your entire journey was booked under a single reservation (PNR). In this case, when you check in for your first flight—whether online or at the airport—the airline will issue all of your boarding passes through to your final destination, and your luggage will be "through-checked." However, in 2026, there are two major exceptions. First, if you are flying on "self-transfer" tickets (booked via sites like Kiwi or as separate one-way tickets), you must exit the secure area, collect your bags, and check in again at the ticket counter for the next airline. Second, for certain international-to-domestic connections (notably in the U.S.), you must "collect" your bag after customs and drop it on a re-check belt, though you usually don't need a new boarding pass. Always check your mobile app during your layover; if your gate has changed or a document check is required, the app will prompt you to "check in" or see an agent.