To achieve this, the manifacturers of DVD hardware and software have agreed to define seven regions (also known as 'zones' or 'locales') and assign them to world territories as follows:
Not all discs are region encoded. Some DVDs are meant to be viewable on any player and are usually known as region-free (or 'region 0'). Additionally, in some countries you can legally purchase DVD players that are designed or modified to be 'region free' and will play DVDs regardless of their regional encoding.
Keep in mind that in addition to regional encoding, there are also differences in video/TV standards from one country to another. Video information on DVD is usually formatted for a specific television system: NTSC (used in the United States) or PAL (Europe). These two standards are incompatible.
Even if a disc is region free, you need to make sure your TV and DVD player can handle its video format. Normally, an american (NTSC) television will not be able to display a disc in PAL format and vice versa. However, many European TV sets are multistandard (and can display a NTSC signal). Also, some DVD players include features to convert a video signal from one standard to another. If you plan to buy videos or DVDs from another country, you need to make sure that your player and TV hardware can properly handle the different video standard.