Quest giver

Quest givers are NPCs that provide quests for players. When the quests are completed, the quest giver will usually bestow XP, or, if the character is the maximum level obtainable, money. Sometimes, quest givers will include an item or two as a token of their thanks. Questgiving NPCs will not usually attack monsters or the opposing faction unless they have been attacked first ( is an exception, because he will attack mobs that follow you inside the ziggurat).

Identifying quest givers
A quest giver who currently has a quest for you will have a golden exclamation point above their head and will appear on the minimap as small golden exclamation point. A silver exclamation point above a quest giver shows a quest that will not be available to you for a few more levels. A blue exclamation point or question mark  indicates a repeatable quest.

As of Patch 2.3, your pointer will also change when you move it over a quest giver:
 * [[File:Pointer quest on 32x32.png]] interact with quest giver    [[File:Pointer quest off 32x32.png]] quest giver out of range

Some items and fixed devices can be quest givers also. Usually, you need to right-click the item or fixed device to get the quest. Items like this will usually say "This Item Begins a Quest" in their tooltip. The only way to tell if a fixed device begins a quest is to interact with it.

As of patch 3.3.3 items, which give quests, were made more noticeable by having a large golden exclamation point on the left side of the icon.

Quest enders
Most (but not all) quest givers are also quest enders (who you turn the quest items to or receive the quest reward from).