There are two main types of quests in Sacred: Main Quests and Side Quests.
Main Quests are quests that you play in a specific order throughout a Campaign in Single Player (although you can play through the Underworld Campaign in a multi-player game). You must complete all of these quests to complete or "beat" the game.
Side Quests are optional quests that you can undertake by talking to NPCs throughout the game and can usually* be taken in any order at any time throughout the game in Single Player or Multi-player.
Side Quests are your average run-of-the-mill quests that you can take part in by talking to an NPC with a ?! symbol over their heads. They are usually very simple and quick to complete. You will earn experience, some gold and be given a reward by the quest giver upon completion. Usually the item given is a rune or a ring. Occasionally, a Set Item will also be given.
Some Side Quests do not appear in the quest log or have quest flags associated with them. These quests have no name, but they have been given names here on the wiki such as Seraphim Rescue, Holiday Makers, Tarek the Minotaur, etc. Some people just consider these to be Easter Eggs; they have one thing in common with all side quests, however, in that the quest giver will give you a reward upon completion.
The following is a list of Skill/Attribute Quests in Sacred:
Series Quests are unique in the fact that there are more than one quest linked together in a series. These are the only quests that must be done in order. You won't even find the starting NPC for the next quest in the series until you have completed the current step. Now these are tricky because sometimes you may encounter an NPC that gives you a quests and then immediately upon getting your reward they will once again have the ?! above their heads letting you know they have something new for you to do. But other times you just have to take a chance and speak to them again to find out. Worse still there are times that the next quest is given by a different NPC in a totally different area... therefore you have to go hunting for them and if you don't happen to run across them you would never know there was another part. (NOTE: Further down I will give a quick reference list of the Series Quests that don't have the same NPC or the NPC gives you another part in a different location. The obvious ones I have just listed normally in the quest lists.)
The following is a list of Series Quests in Sacred:
Character-Specific Quests are some more average quests like any other except for the fact that they are only available to certain character classes.
The following is a list of Character-Specific Quests in Sacred:
Region Boss Quests
Region Boss Quests are quests that only appear once you have reached 0 (or 999?) in the kill counter. The kill counter is a gauge that appears in the corner of your mini-map when you hit Tab, it shows the total number of enemies in a region and has a countdown of that number as you defeat enemies. When you reach 0 a quest flag will appear in that region to show you where the region boss enemies have spawned. They are a large group of unique boss monsters that you must kill to "Clear the Region". These monsters will always spawn at the same location in any given region.
One last note, side quest can also fall into more than one of the categories above. For instance, Intrigues is a series but also rewards a skill point at the end so it is both a Series quest and a Skill/Attribute quest.
Quest rewards can include experience points, gold, armor, weapons, runes or jewelry. To some extent the reward is random (chosen from a pool of items), so you can quicksave before turning in a quest and reload until you receive e.g. the one rune you are searching for. Given the quantities of xp and gold you earn in battles, these quest rewards are negligible, the important rewards are (possibly) the items.