From Diablo Wiki
Set Items comprise Item Sets. In Diablo III these are not a separate type of item, but function basically as groups of Legendary items that grant additional bonuses when equipped at the same time.
Set Items are primarily end game gear, and while the properties of any individual set item might not be that great, they can be quite powerful when used in pairs or groups, when the partial set bonuses are included.
All Set Items that can be found exist only in Inferno, with a level 60 requirement to equip. Other Set Items can only be created via crafting with the Blacksmith, and those range widely in their level requirement and stats.
- Diablo II featured item sets as well. See the D2 for details.
 Item Sets List
A list of every item set in Diablo III, including the individual items in that set and the partial set bonuses. Hover on the "db" links to see the item tooltips, pulled from the game files via DiabloNut.IncGamers.com.
 "Found" Item Sets
Item sets where the items can only be found from monsters or objects in the dungeons (or bought from the Auction House). All of these sets have a level requirement of 60.
|Immortal King's Legend||
|Legacy of Wicked Dreams:||
|Shenlong's Noble Path||
|Tal Rasha's Sacrifice||
 Crafted Sets
 Item Set Appearance
Most of the Item Sets in Diablo III grant a special appearance to the character wearing them. A few of the individual items do this, but full sets do it more visibly, with graphics or special functions only granted by that set. Individual set items often have unchanged graphics, but offer new colors and other visual effects.
Below is an image of the Aughild's Treasured set worn across every class:
 Item Sets During Development
During Diablo III's production, the developers frequently mentioned their desire to completely change around Item Sets to be more useful during the leveling process, and to be more consistent in item level and quality. (Item Sets in D2 often had items that varied hugely in level and utility and could thus seldom be worn usefully at the same time.)
We have a few ideas still that could allow them to be available while leveling, but each of them have sticking points that would require their own solutions. One is expanding sets out so that it isn't just one item in each slot, but a group of items all separated by level requirement. So there could be, say, five pairs of pants that all work as part of the set and are each better than the last. While leveling you could be wearing the first pair of pants and then find a new and better pair that still work to benefit your set bonus. That isn't without its problems though.
We of course like and intend to keep partial set bonuses, by the way.Anyway, sets are actually in the game right now in very limited forms, there's a bit of design left on them yet, but as I said they work very well at end-game and that's where we're leaning toward them appearing.
Bashiok added an update six months later, in April 2011.
Bashiok: Set items are now legendaries defined by a set bonus. They’re crafted items while leveling (recipes can be found that grant the ability to craft all the items in a set), which allows someone to really invest in filling out a set before they out-level it. Then at max level we’ll drop set pieces normally.
Leveling up you will find recipes that will enable you to make a set. Every item in that set will be in the recipe list, enabling you to craft the set one piece at a time. When you hit max level, you will find the actual set pieces, not the recipes for the complete sets… That’s how I understood it.
 Diablo II Item Set Issues
Item Sets and Set Items were a nifty idea in Diablo II, but the execution was not perfect, especially in D2C, where Item Sets were generally underpowered and not worth wearing. There were no partial set bonuses in D2C; a character had to wear the entire set to receive any bonuses, and these bonuses were generally quite small.
D2X introduced much higher quality item sets, including ones comprised entirely of exceptional or elite items, some of which were comparable to the best Rare or Unique items. D2X also incorporated a variety of partial set bonuses, where characters drew extra bonuses for wearing two or more items of a set.
The main problems, though, of characters finding it too difficult to find some or all of the same set, remained. Jay Wilson spoke to this in a December 2008 interview with 1up.com. 
- ↑ Blue forum post - IncGamers June 3, 2011
- ↑ Jay Wilson Interview - inDiablo.de, August 2010
- ↑ Blue forum post - IncGamers November 11, 2010
- ↑ Bashiok forum post - Dizblo.IncGamers.com, April 2011
- ↑ Jay Wilson Interview - 1up.com, December, 2008
|Items of Diablo III  Item Basics Normal Items Legendary Armor I Legendary Armor II Legendary Weapons 1h Legendary Weapons 2h Item Sets|
|Item Basics||Item Modifiers||Inventory||Artisans||Merchants||Miscellaneous |
|Armor - Class-Specific||Weapons - Class-Specific||Crafting Items||Other Items |
|| • Blacksmith Plans
|Waist||Wrists & Hands||Legs & Feet||Head |
|| Voodoo Masks - WD|
| Chest Armor
|| Amulets cont.
|| Rings cont.
40) Puzzle Ring
|| Sources - Wiz|
|| Fist Weapons - Monk
|| Mighty Weapons - Barb|
|| Daibos - Monk
|| Bows |
|Item Sets |