DVDs and DVD players are split into "regions" numbered 1 to 8, and players assigned to certain regions cannot play DVDs from other regions. However, most DVD players have secret menus where you can disable regional encryption, allowing you to play any movie from any region.
Go to your DVD player and write down the model number. This number may be on the front or the back of your player. It is usually a combination of numbers and letters, such as "H1080R" or "DVP3310."
Go to the Video Help DVD Hack page (see link in Resources) and search for your DVD player by model number. When you find your player, follow the instructions listed.
Enter the secret code provided by the hack page. After entering the code you'll be able to choose multiple regions. Switch it to region 0 instead of region 1; this will allow you to play DVDs from all regions.
If you can't find your player's hack on this page, type the model number into a search engine with the word "hack" after it.
Not all players have hacks, so you might be out of luck. Accessing the region menu will usually void your player's warranty.