In order to play DVDs, you need to have the right codecs installed. A codec is some software that allows applications to read a video or audio format. If you try to play a DVD and don't have the right codecs installed, the movie player you're using should inform you and offer to install them for you. If it doesn't happen, you'll have to install the codecs manually - ask for help on how to do this using your Linux distribution's support forums or otherwise. The software packages you'll probably need are gstreamer0.10-plugins-ugly and libdvd0.

DVDs are also "copy-protected" using a system called CSS. This prevents you from copying DVDs, but it also prevents you from playing them unless you have some extra software to handle the copy protection.

You can install a program called deCSS to handle the copy protection. You will need to find specific installation instructions for your Linux distribution. Unfortunately, this cannot be used in some countries because the way it gets around the copy protection is illegal there.

You can buy a commercial DVD decoder that can handle copy protection from Fluendo. It works with Linux and should be legal to use in all countries.

DVDs have a "region code", which tells you in which region of the world you are allowed to play the DVD. DVD players can only play DVDs from the same region as them. For example, if you have a region 1 DVD player, you will only be allowed to play DVDs from North America.

If the region of your computer's DVD player and the DVD you are trying to play do not match, you won't be able to play the DVD. It is often possible to change the region used by your DVD player, but you can only do this a few times before it locks into one region permanently.

To change the DVD region of your computer's DVD player, use regionset.