If you are flying on a codeshare flight between Virgin Atlantic and Delta Air Lines, the golden rule is to check in with the "operating carrier"—the airline that actually owns and flies the airplane you are stepping onto. You can find this on your confirmation email or boarding pass under the phrase "Operated by..." or "Flight [Number] operated by [Airline]." For example, if you booked through Virgin but the flight is operated by Delta, you should use the Delta app or website to check in 24 hours before departure. If you are checking in at the airport, you must go to the desk of the airline that is flying the plane. While the two airlines share a deep partnership and allow you to earn miles on either program, their computer systems are still distinct for the check-in process. If your journey involves multiple legs with different airlines (e.g., a Delta flight to London and then a Virgin flight to Africa), you will typically check in with the first airline for the entire journey, but you should always double-check your terminal and desk information to avoid a last-minute dash between buildings.