[[File:Aeroporto de Brasilia.JPG|thumb|Check in at [[Brasilia]]'s airport]]
The flight ticket itself does not enable you to board the plane; for this, you need a '''boarding pass'''. '''Check- in''' is the process of producing your boarding pass, which includes seat numbers, departure times and gates. In the security check , only passengers with boarding passes are admitted into what is called the airside section or the transit area. You can often do the check-in yourself electronically, either on -line or with check-in kiosks at the airport. Check-in is not to be confused with '''baggage drop''', which requires prior check-in.
Check-in is handled by the carrier's ground staff or its representatives. Some airlines allow (or sometimes require) you to check in '''on-line''', often within 24 hours before scheduled departure, and some no- frills carriers such as Ryanair will even charge you a hefty fee if you fail to do so. On- line check in can often be done through the airline's website, or sometimes by smartphone app. Apart from the booking reference or e- ticket number you also identify yourself by frequent-flier or credit card number or by giving personal details. Upon completed check-in you will often be sent a boarding pass to print out by yourself; again, failing to do so may result in surcharges from some low-cost carriers. If you enter the correct information but are denied check- in, your flight may have been cancelled or the reservation modified by the airline; in that case it is wise to contact the airline immediately, preferably before travelling to the airport.
If you have not done so electronically/remotely, the first thing you will need to do at the airport is '''check in''' for your flight. Present your ticket (if you don't have an electronic ticket) and some form of ID (passport if travelling internationally) to airline staff at your flight's designated check-in counter or at common check-in counter, depending on your airline.
You will typically have to '''queue''' before check-in: on very full flights and very busy days this alone could take more than an hour, particularly for international flights. There are usually separate, and much shorter, check-in lanes for first, business class passengers, upper tier members of the airline's frequent flyer program (eg: silver, gold) and sometimes those who checked-in through remote methods (eg: on-line check-in). If the queue is long and your flight is leaving within the hour, your flight status is already showing "Go to gate" or you are approaching the check-in deadline for your ticket, let airport staff know as they will often allow you to go to the front of the queue and check in immediately. Sometimes they will specifically ask for passengers for a flight that is about to close to make themselves known so that they can check them in right away, but sometimes they will not. Discount airlines have the strictest check in deadlines and some will not allow you to check in after the deadline even if you made it to the end of the queue in time. * You may face the same challenges in lines/queues for the personal security screening. If time is short, use the same methods as for check-in to get help.
With some airlines you will receive a '''boarding pass''' with a seat assignment, while some do not assign seats. You will need a boarding pass to present to the security staff and later to the gate staff when boarding the flight. At this time, your checked luggage will be weighed, labelled, and handed off to baggage handlers.
Some airports offer curbside check-in, which allows you to check-in your bags before entering the terminal. These are normally available on domestic US flights and do what the standard check-in counters inside do except that they will not issue boarding passes to you. You will have to obtain them inside if you haven't done so from on-line check-in. Curbside check-in is offered nowadays for a fee levied by the carrier, sometimes on top of prevailing check-in baggage fees. Moreover, tips for the staff are expected.
The check-in staff will print a bar-coded luggage tag once your bags are processed; the longer part of it will be attached to your luggage while the shorter part will be given to you. Keep this, as upon arrival, some airports may require passengers to present these along with their luggage to ensure that the person carrying the luggage is indeed the owner. These luggage tags are also useful if you suspect some of your check-in luggage is missing or similar to other luggage. Before the ticket agent attaches the new luggage tags for your upcoming flight, be sure: * You've removed any old airline tags. * Your new tag(s) reflect your destination airport. ..checked-through as below.
In case your journey for the day involves several flights, you may want to request to have your baggage '''checked- through'''. Check-through is when your baggage will be tagged all the way until the last leg of your journey and in most cases, you do not need to claim your baggage in your intermediate stopovers any more (especially for international-international or domestic-domestic flights on full-service carriers; does not apply to international-domestic connections). You need to inform the check-in staff of the flights which will be covered by check-through for a particular journey as they can't assume that's your preference. However, check-through is ''not always'' possible, make sure you inquire of the check-in staff. You may check the section "Making a connection" below and are advised to contact the carriers concerned for more information on when check-through may or may not be possible.
An increasing number of airlines are implementing a '''self-check-in ''' system at certain airports. In most cases this option is available to passengers with or without check-in bags. These systems involve small kiosks in which you can enter your booking reference, swipe/insert the credit card used to make the booking or swipe/insert your frequent flyer card (if it has a magnetic strip) to access your record and print out a boarding pass for you and your travelling party. You may have the opportunity to change your seats when checking in; in particular, many airlines do not open the exit rows until the day of the flight. In recent times though the self service check- in kiosks of some carriers have been extended to include features that allow passengers to check-in baggage by themselves.
A good number of carriers also offer checking-in via mobile phone either by visiting the mobile website or downloading a specific app on your smartphone. At the end of the process, some carriers may give you the option of being issued a mobile boarding pass depending on your origin and destination, though carriers that offer them usually don't do so for international flights. You don't need to print your mobile boarding pass, just present it to security and airline staff. Check with the carrier you are flying with to see which devices are supported. As mentioned earlier, if you checked-in via kiosk or on-line, the airline usually provides a special lane for you where the rest of the check-in process will be expedited. At this counter, please provide the information and documents that were given to and/or requested of you. Some carriers require passengers who used self check-in to proceed to designated check-in counters to have documents verified, even if they do not have check-in bags. In other cases though, especially for intra-Europe travel in economy class, the counters are only designated as baggage drop-off points: you should have checked-in either online or using the kiosks before queueing. Electronic check-in is possible only in routine cases; if there are special needs or inconsistencies with the tickets (such as mismatches with names), only manual check-in at the counter is possible.