United Airlines offers multiple check-in options to accommodate passengers' preferences and needs. Online check-in is available starting 24 hours before your flight's scheduled departure and closes 45 minutes prior for domestic flights and 60 minutes for international flights. This option allows you to select seats, pay for checked baggage, and receive a mobile boarding pass. If you choose to check in at the airport, you can use a self-service kiosk or visit the ticket counter. Kiosks are accessible from 24 hours before the flight and close 45 minutes before departure for domestic flights and 60 minutes for international ones. At the ticket counter, check-in is available from 45 minutes to 4 hours before departure, depending on your destination. For curbside check-in, available at many U.S. airports, you can check in from 45 minutes to 4 hours before departure. When checking in at the airport, ensure you have a valid government-issued ID for domestic flights or a passport and any necessary visas for international travel. If you're traveling with checked baggage, it's advisable to arrive at the airport at least 2 hours before a domestic flight and 3 hours before an international flight to allow ample time for check-in and security procedures. Remember to have your boarding pass and ID ready for inspection at the security checkpoint and boarding gate. By utilizing these check-in options and adhering to the recommended timelines, you can ensure a smooth and efficient start to your journey with United Airlines.