There are basically three different types of airline tickets: Round Trip, One-Way and Open-Ended. It is important you understand the benefits and disadvantages of purchasing each ticket before doing so.
Round Trip Tickets are usually the cheapest and most common tickets purchased. However, unless you already know how long you’re going to be able to travel, they are somewhat limiting, because you have to pick a return date when you book the ticket. One thing worth looking into when purchasing a Round Trip Ticket is how much it costs to change the return date of a flight. Depending on the airline and time of travel these fees can be as low as $25, but at times can be as high as $200.
One-Way Tickets are usually going to be more expensive than round-trip tickets. Also, you need to be aware that flights booked at different times of the year can widely vary in cost even if you’re coming and going from the same location. However, booking a One-Way Ticket does give you the flexibility to not only come and go as you please, but also to depart from any city or country you may end up at. This type of ticket would be most useful for someone who plans on traveling after their program, but is unsure of exactly where they will end up. It is important you investigate whether or not the country in which you’re studying requires proof of a return flight as part of their immigration procedure.
Open-Ended Tickets will give you almost as much flexibility as a one-way ticket, but it will additionally offer you a way to get home on a moment’s notice if, for some reason, you have to or choose to. Instead of your return ticket specifying a date, you have the option of using it whenever you and the airline agree, within a certain period of time (usually about one year, but details may vary). This is potentially your most expensive option, but every airline is different so you will need to compare prices. It may make the most sense to estimate when you think you’ll want to return and buy your round trip ticket. Remember you can always pay a fee to switch your return date.