Player-versus-Player Combat

Player-versus-player gameplay is very important to World of Warcraft. However, the designers are mindful that players are very divided about this issue. Thus, Blizzard is made sure that there are two different Realm types at launch. On the normal Realms, PvP combat is entirely consensual. You cannot be attacked by other players unless you want to be. The other Realm type is player-versus-player, and on this server, you can sometimes be attacked by players of the opposing faction without warning.
On normal Realms, you can enter into player-versus-player combat by storming enemy capitals, entering special PvP zones called battlegrounds, or by attacking the guards in enemy cities. In all cases, you have a choice to engage in PvP combat or not.
On PvP servers, there are many zones that are flagged as contested territory. In these zones, players from opposing factions can attack each other freely. Thus, you could be fighting monsters by yourself, only to be killed by a stealthed enemy rogue. PvP Realms also enable PvP combat through Battlegrounds, attacking enemy guards, and entering enemy capitals.

The rewards for PvP play are excellent, however. Blizzard wants to encourage players to participate in PvP, since the Horde-Alliance conflict is central to the Warcraft universe. As you kill enemy players, you will accumulate honor points, which enable you to purchase rewards from special PvP vendors located in Stormwind and Orgrimmar. As you accumulate more honor points, you will gain certain benefits, such as special equipment, weapons, and mounts. Keep in mind though, that you will only gain points for killing players near your level. Blizzard will not reward players who attack lower-level characters.