D&D Insider (DDI) was Wizards of the Coast's subscription method of digitally delivering periodic content, information, and online tools for the 4th Edition of Dungeons & Dragons to the game's players from 2008 to 2014. The service officially shut down in 2020.

Shannon Appelcline, in the book Designers & Dragons (2014), stated that in 2005 Hasbro decided all of its core brands "needed to earn at least $50 million dollars a year" which would be a struggle for the Dungeons & Dragons brand, as it "was probably grossing just $25 or $30 million at the time — in large part because" subsidiary Wizards of the Coast didn't have the computer game rights for the brand. Brands that didn't meet the minimum to be a core brand would not receive good support for expansion and development. This led Wizards of the Coast to launch a digital initiative, initially presented to Hasbro in 2006, where the next edition of the game would "be created with the specific intent of integrating it with an online service that would include a virtual tabletop for play". If Wizards could "convert a fraction of D&D's players to paying online subscribers", then Dungeons & Dragons "would hit its $50 million dollar goal" and become a core brand. Wizards of the Coast developed D&D Insider and Gleemax, a community hub and launcher for all of Wizards of the Coast's games, as the two digital aspects of this initiative.

D&D Insider was announced at the August 2007 Gen Con as a subscription-based electronic supplement to the upcoming 4th Edition of Dungeons & Dragons. The demo included a short video of a virtual "dungeon" (called the Game Table) in which some D&D adventures take place, containing virtual miniatures based on player characters created in the Character Visualizer (a 3D full-body portrait program). Randy Buehler, vice-president of digital gaming at Wizards of the Coast in 2008, told BBC News that "if we want to recruit the next generation of gamers we have to be online, that's clearly the platform where people have chosen to play. [...] The idea is that you can play it as 100% table-top experience, or 100% electronic or somewhere in between".

DDI officially launched in 2008 with the start of the new edition. However, it was launched without the advertised virtual tabletop (VTT) component and other digital toolsets. While it was also announced in 2007, many features for Gleemax were delayed before it was cancelled in July 2008.

DDI launched their subscription service in October 2008 which initially included articles, archived Dragon and Dungeon web content, and a compendium of rules elements for the 4th edition of Dungeons & Dragons. Appelcline commented that Wizards of the Coast's roleplaying group had issues with the D&D Insider Compendium as the sentiment was "it took all of their core book material and gave it away online". The money from user subscriptions initially went to "the digital group, not the roleplaying group, causing problems within Hasbro's bureaucracy. As a result, the RPG division had to take over Insider, but still found themselves supporting a product that they weren't sure was in their best interests". Additionally, a consolidation of digital initiatives by Wizards of the Coast led to layoffs of members in the digital group in December 2008. This included Buehler along with Andrew Finch (Director of Digital Games), William Meyers (Creative Manager of Digital Design) and Jennifer Paige (Online Community Manager).

In February 2009, the Character Builder was launched and required downloading an application limited to Windows machines. After November 2010, the Character Builder become browser based and required Microsoft Silverlight. The Character Builder only supported official Wizards of the Coast content. In January 2011, DDI removed the option of downloading the Dragon and Dungeon magazines as formatted PDFs. A Monster Builder (as part of the Adventure Tools suite) was also released in 2011. While the VTT went into beta-testing for DDI subscribers in 2010, the VTT was officially canceled in 2012.

Mike Mearls, in a January 2012 interview on the next edition of Dungeons & Dragons, stated that they planned "to continue offering people access to tools like the D&D: Character Builder and the D&D: Monster Builder to support 4th edition". In 2014, the service was discontinued. A subscription renewal email from Wizards of the Coast indicated that the DDI subscription would no longer include new issues of Dragon and Dungeon magazines (only archives), and the online resources would no longer be actively supported. While existing subscribers could renew the service, DDI stopped accepting new subscribers. The service was officially shutdown on January 1, 2020 due to Microsoft Silverlight no longer being supported.

Michael Zenke, for Wired in June 2008, described DDI as a "storehouse of knowledge for players and dungeon masters". Zenke highlighted that the subscription cost at launch was roughly the same cost as previous subscription costs to print magazines Dungeon and Dragon so DDI was "great value for the money" since it included both the electronic editions of the magazines along with other online tools. However, Zenke also felt that "for a hobby that has (despite the high prices of the actual D&D books) mostly been a fairly cheap pastime, D&DI's pricing is tantamount to highway robbery" as every player in a group would need to pay to access the online services. The other major problem for Zenke was that DDI launched without the "D&D Game Table" component. Zenke thought DDI "should be a tremendous service" as no VTT product had "this level of sophistication" before and no other product had ever "been tied into the core game the way D&DI is, nor coupled with the Dungeon and Dragon magazines – respected publications with a long history of serving the D&D community".