Sometimes a session of D&D is a complete game in itself (often called a “one-shot”), where you play a short adventure that lasts for just one session. More often, though, D&D sessions are connected in a longer adventure that takes several sessions to complete, and adventures can be strung together into a larger narrative called a campaign.
A campaign is like a TV series, while an adventure is like a season of the series. And a game session is like a single episode—it might be self-contained, but it usually links to the larger plot if there is one.
An adventure might be created by the Dungeon Master or purchased (the examples of play in this chapter are inspired by a published adventure, Curse of Strahd). In either case, an adventure features a fantastic setting, such as an underground dungeon, a wondrous wilderness, or a magic-filled city. It includes a cast of nonplayer characters controlled by the DM. Often one of the NPCs is a villain whose agenda drives much of an adventure’s action.
During an adventure, the adventurers explore environments, events, and creatures presented by the DM. Battles, traps, negotiations, mysteries, and more arise during these explorations.
Adventures vary in length and complexity. A short adventure might present only a few challenges and take only one session to complete. A long adventure might involve many combats, interactions, and other challenges and take dozens of sessions.
A campaign is a series of adventures with a consistent group of adventurers following the narrative.
Some campaigns are episodic, where each adventure is its own tale and not much besides the player characters links it to the next one. Other campaigns involve long-running plots, a cast of recurring NPCs, and themes that span multiple adventures, leading toward a climactic conclusion.
As with adventures, a DM might create a campaign from scratch, assemble a campaign from published adventures, or mix homemade material with published material. And the campaign might take place in a world of the DM’s creation or in a published campaign setting, such as the Forgotten Realms or Greyhawk (the latter is described in the Dungeon Master’s Guide).