A much disputed encoding can be used to encode DVD's to work only in certain regions. The global encoding standard was initiated by the film studios and publishers to prevent piracy and - according to critics - control pricing and timing of releases.
DVD players supporting multiple or all regions are available (frequently referred to as "region-free"). However, it is recommended to check the encoding region before buying DVD's from other regions. Certain DVD players allow you to change regions, but only a certain amount of times (region-locking), and there is a counter on the DVD device to ensure that changes are only made few times.