Turbine releases major content updates to the game as "modules", named after the module concept in the pen-and-paper version of D&D. Additional content is release between modules as "updates"
Module 1: Dragon's Vault
On April 5 2006 Turbine released its first module, "Dragon's Vault," which included a new dungeon; this new area included additional content and quests as well as the chance for players to battle a red dragon. Also included were a number of fixes to the combat system and minor tweaks to the user interface.
Update 1.1: The Harbor
This first update include changes to the low level Harbor quests.
Update 1.2: Solo Enhancements
More changes to the Harbor area, including the addition of several solo-only quests there.
Module 2: Twilight Forge
The "Twilight Forge" module, released July 12 2006, added a new player race: the Drow (playable only if certain requirements have been met), as well as new enhancements, spells, a patron system, in-game mail, and adventures set in the Restless Isles, a new outdoor area.
Update 2.1: Litany of the Dead Part 1: The Necropolis
In August 2006, an update called "Litany of the Dead Part 1: The Necropolis" was released. This update is the first part of the Litany of the Dead series that carried into next year. The update has five full quests as part of the first part of Litany, and culminates in an encounter with a powerful vampire.
Update 2.2: Stormreach Under Siege!
This update for September 2006 introduced the first quests above level 10, other than the Twilight Forge raid, including a level 12 quest in the previously low-level only Harbor area.
Module 3: Demon Sands
This module, the largest one at the time, was released on October 25, 2006. With this update, Turbine attempted to alleviate many of the player base's most acute concerns. Primarily, it introduced some more meaningfully explorable areas to the game in order to give the world a feeling of greater breadth. It also introduced some consensual PvP (Player vs. Player) elements to the game (in the form of "Tavern Brawl" arenas and objective-based quests; Capture the Flag, Indoor and Outdoor Deathmatch), as well as an auction house, and the first level-cap raise from ten to twelve.
Update 3.1: Evil Resurgent
This December 2006 update included a rework of the social panel, many bug fixes, and six high level quests. Most of these new quests, all of which are rated at level 11, are sequels to previous quests, extending the storylines of the characters involved.
Update 3.2: Litany of the Dead Part 2
Five new monsters (phase spiders, shadows, umbral worgs, umbral gargoyles, and invisible stalkers) were released in this update, along with five quests for party level 8-9. These quests continue the storyline of The Necropolis from Litany of the Dead Part 1.
Update 3.3: Academy Training
This update completely revamped the Action Point enhancement system. Also, in celebration of DDO's one-year anniversary, all chests were at +1 level from 2/28 to 3/4, and all xp awarded from 3/2 to 3/4 was +50%.
Module 4: Reaver's Bane
April 2007's new module, Reaver's Bane, brings the level cap up to 14 from 12, and introduces a new terrain mechanic along with many new spells and abilities for characters of all levels. Two new areas (the Cerulean Hills and Gianthold Ruins) use the new mechanic that includes entrances to traditional quests, plus 3 new types of quests. The new quest types are slayer quest (where you get experience for how many monsters you or your party have killed), explorer quests (where you get experience just for visiting a new part of the area for the first time) and rare encounter quests (where you get experience for killing infrequently spawned named monsters).
Update 4.1: Mark of the Dragon
The May 2007 update included, among other things, the implementation of Dragonmarks and the addition of a new encounter area: Ataraxia's Haven.
Update 4.2: Searing Heights
This July 2007 update revamped the Menechtarun desert landscape and the Waterworks adventure area. There is an added landscape for level 4 characters to battle the Sulatar firebinders, new spells, abilities, and enhancements including Holy Sword and Warchanter. Players get 3 more weapon set configuration slots, for a total of 7. Also fixed were several bugs. Many new spells were added for all spellcasting classes. Extra enhancements were also added. One additional level 4 dungeon was added.
Module 5: The Accursed Ascension
This new module, released in September 2007, includes parts 3 and 4 of the Litany of the Dead; by doing so, it doubled the amount of quests in the Necropolis area. It ends with a new high level raid. Apart from the addition of new enhancements and some minor corrections, the metamagic system went through a major revision and the item tooltips were vastly improved. Some new additions are collectable and gem bags, made to reduce the cluttering of inventory space.
Unlike previous Modules, the development team will not release interim updates. Responding to the players' feedback that the interim updates do not provide enough new content, the developers will instead focus on creating significantly larger Modules.
Module 6: The Thirteenth Eclipse
The January 2008 update, the Thirteenth Eclipse, raised the level cap from 14 to 16, and opened a previously locked area that was partially accessible by players, The Twelve. Also with this area is a new set of quests and a new raid located in an area connected to The Twelve, called the Vale of Twilight. Included as well with this update is allowance for subscribers to customize the player interface as is available in Turbine's other MMO "Lord of the Rings Online".
Update 6.1 (released on 27th February 2008) introduced a new, ongoing live event, as well as a slice of anniversary cake. The anniversary cake summons a Djinni that will grant a wish (as the Wish spell)
Module 7: Way of the Monk
This update, released on 3 June 2008, introduced the Monk class to all servers. It had previously been in testing for a time on the Risia preview server. Included were various city upgrades, bounty subquests that involve collecting remains of monsters, and UI interface tweaks. The Monk class is planned to be updated in the near future.