There will be both PvP and PvE in this game. PvP is confined to the central province of Cyrodiil and will involve the succession war to determine the next emperor.
If you do not wish to fight other players, then you will be able to play a strictly player-verus-environment game, alone or with friends, in your chosen faction's land. NPCs that you can kill will likely be plot oriented, and as I understand it, if you've killed any of them, they will only be dead for you.
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For anyone who is interested in reviewing the information that has been released thus far about The Elder Scrolls Online, there is pretty useful information on a page over at http://tamrielfoundry.com/ that aggregates most of that information all into once place. The http://tamrielfoundry.com/development-faq/ has references to most of the articles that have been released, and is useful for getting a feel for the general direction of the game. Hopefully this stays updated as more info comes out. I thought that this would be a nice piece of information to share for anyone following ESO.
The Development FAQ contains information such as:
- General Gameplay
- Player Factions
- Classes
- PvE Info
- PvP Info
- NPC Guilds
- Crafting
- Player Guilds