This question already has an answer here:

Do I have to restart my world in order to get new features added to the game or does my world, before the update, gain the features on it's own?

marked as duplicate by SevenSidedDie, Schism, Ullallulloo, Frank, JohnoBoy Jul 2 '13 at 5:38

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • I'm sorry, I did not know there was another question with the same topic as mines. I am new to this website and did not know how to find if there was questions I wanted to ask. – user50331 Jul 2 '13 at 4:38
  • That is ok! Posting a duplicate is one of the appropriate ways to discover if your question has already been asked, if searching for it turned up nothing. :) – SevenSidedDie Jul 2 '13 at 14:22

I assume you are talking about basic minecraft, no mods and the like.

The world itself that is already generated will remain as it is. It will not gain any of the new spawns and the like to be found within the world. When you explore a new area however, new content will be generated in those chunks giving you access to the new items.

If you are talking about mods then the answer is too varied. There are some mods that can 'regenerate' in existing areas certain aspects of themselves but this is not a universal part of all mods.

  • Thank you, I was looking forward to the new horse mobs, and had found them in my old world after this asking this question. – user50331 Jul 2 '13 at 4:37

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