Blu-ray is a region encoded format in the same way that DVDs are. This means that you will have to buy discs from the same region that you bought your Blu-ray player from.
Normally this is not an issue as most people will buy their player and their discs from their own country and won’t even have to think about this restriction.
However, some collectors find that one country will release a better version of a movie than their own with perhaps with more extras or better packaging for example. If you are serious about your collection, or perhaps you do a lot of travelling and buy discs abroad, you may want think about getting a multi-region or ‘unlocked’ player, or one that can be unlocked afterwards with a special code you type in through the remote.
The regions are:
Some discs will be ‘region free’ or ‘region 0’ meaning they will play on any Blu-ray player.
This is also backwards compatible, meaning that region encoded DVDs will also need to be the same region as the Blu-ray player.