The Development Team continually expands City of Heroes with free downloadable patches/updates as well as massive free expansions dubbed "Issues." This is because the games are intended to have the feel of comic books, and the expansions being called issues reflects this fact. City of Villains was released as an expansion and stand-alone game, a concept which has been dubbed "Expanshalone." Guild Wars uses a similar system with its additions. The Development Team had planned on releasing a retail expansion to the game (similar to World of Warcraft and its retail expansion The Burning Crusade), but the idea was scrapped, and the content that had been planned to be released in the retail expansion will instead be released among several future free Issues.
Issues
  Issue #1, "Through the Looking Glass", raised the level cap from 40 to 50, introduced several new enemy groups and the Rikti Crash Site and Peregrine Island zones for these levels, and added tailor shops where players can alter their characters' costumes for a fee.
  Issue #2, "Shadows of the Past", introduced the ability for players to earn capes and auras for their characters, respecification, badges for achieving various things in the game, and two new zones, the Hollows and the Shadow Shard, with new enemy groups which appeared in these zones. A small, hidden dance club, the Paragon Dance Party, was also added.
  Issue #3, "A Council of War", introduced a new zone, Striga Isle, replaced the Nazi-themed Fifth Column enemy group with the Council, added several new giant monsters and zone events, added the Peacebringer and Warshade Epic Archetypes for players who had reached level 50 on another character, and added Ancillary Power Pools for characters above level 40.
  Issue #4, "Coliseum", introduced City of Heroes' first player versus player content in the form of an arena, and also added a wide variety of new costume options as well as finer tuning of body and face scale than was previously possible.
  Issue #5, "A Forest of Dread", introduced one new zone, Croatoa, with several new associated enemy groups; it also added a few more zone events, and new powersets for some Archetypes based on archery and sonic powers.
  Issue #6, "Along Came a Spider", coincided with the release of City of Villains, and brought an overhaul of the game client to improve graphics and add support for dual-core CPUs and 3D sound; it also introduced three shared PvP zones, Bloody Bay, Siren's Call, and Warburg to City of Heroes, and the ability for Super Groups to build bases (though this feature requires ownership of City of Villains). The Paragon Dance Party was removed and replaced with Pocket D, a larger area performing the same function, but open to players of both City of Heroes and City of Villains; however, the factions cannot fight each other there. Finally, Gladiator matches were added to the Arena, where players selected NPCs to battle on their behalf instead of fighting directly.
  Issue #7, "Destiny Manifest", was mostly focused on improvements for City of Villains; it raised the level cap for Villains from 40 to 50, and introduced the new Grandville zone for Villains of that level range, Patron Power Pools (the villainous counterpart to heroes' Ancillary Power Pools), "Mayhem Missions" for Villains of all levels, several new power sets for new Villains, and a fourth PvP zone, Recluse's Victory, for both games. Further graphical improvements to existing City of Heroes content were also made.
  Issue #8, "To Protect and Serve", introduced a Police Scanner for Heroes that provides repeatable missions (similar to the Villains' Newspaper) and "Safeguard Missions" (analogous to the Villains' "Mayhem Missions"), as well as a complete redesign of the Faultline zone and the Veteran Rewards system, which gives special "perks" to players based on how long their accounts have been active.
  Issue #9, "Breakthrough", introduced the Invention system and auction houses; it also revamped the game's single raid encounter and opened it to Villain players as well.
  Issue #10, "Invasion", replaced the old Rikti Crash Site zone with a new Rikti War Zone area, featuring a new raid encounter and cooperative play between both Heroes and Villains, and introduced the Vanguard, an anti-Rikti organization frequently referenced in-game but previously not seen. The Rikti enemy group was also redesigned, and a new world event was added, where the Rikti would stage a mass invasion of a random zone.
  Issue #11, "A Stitch in Time", focuses on time travel; it introduced the new Ouroboros group, and its associated Flashback system for repeating game content which the player has progressed past the level of. It also added customizable weapon graphics for powersets which used drawn weapons, even more powerful Inventions, and two new power sets for a variety of Archetypes.
  Issue #12, "Midnight Hour", introduces the Midnight Squad, another time-travel group; a new zone, the Cimeroran Peninsula, set in ancient Rome; two Villain Epic Archetypes for players who have reached level 50 on a Villain, Blood Widow and Wolf Spider; a minor redesign of the Hollows; and new power sets for almost all Archetypes in both City of Heroes and City of Villains based on powers unique to the other game (a Plant Controller and a Brute with Battle Axe are described; whereas there could only be Plant Dominators and Tankers with Battle Axe before).
The City of Heroes Development Team also initiates events based on North American and European holidays and observances, starting with Halloween in 2004, followed by a Winter Event (eventually becoming a primarily Christmas-themed event), and the newest holiday observance a Valentine's Day event.