What Is Basic Roleplaying (BRP) and How Does It Work?

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Basic Roleplaying (BRP) is Chaosium's generic, setting-agnostic tabletop RPG engine built on percentile (d100) dice rolls. You use it when you want one flexible rulebook to run adventures in any genre—fantasy, horror, science fiction, historical—rather than committing to a game tied to one setting. If you already know you want Lovecraftian horror or Glorantha fantasy specifically, a dedicated Chaosium game is usually the easier entry point; BRP is for groups who want the underlying system and will supply their own world.

The Core Idea: Roll Under a Percentage

BRP's central mechanic is simple: every meaningful capability is rated as a percentage, and you roll d100 trying to land at or under that number. A character with Spot Hidden 65% succeeds on a roll of 65 or less.

This one rule covers combat, skills, and most contested situations, which is why the system is easy to teach and easy to hack. Characteristics (things like Strength, Intelligence, and Dexterity) generate the starting values for skills, and skills improve through play rather than through level-ups.

How Outcomes Are Resolved

Most rolls produce more than a pass/fail:

  • Success — you roll at or under your skill.
  • Failure — you roll above it.
  • Special and critical results — very low rolls (often a fraction of your skill) represent exceptional outcomes, and very high rolls can represent fumbles, depending on the edition and optional rules in use.

Contested actions typically compare the quality of each side's result rather than just who succeeded. This graded-outcome approach is what gives BRP its reputation for grounded, believable results instead of swingy binary luck.

BRP vs. Chaosium's Specific Games

BRP is the engine; Chaosium's flagship games are complete vehicles built on it. The relationship matters when you're choosing where to start.

Basic Roleplaying (BRP) Call of Cthulhu RuneQuest
Scope Generic, any genre Horror / cosmic horror Bronze-Age fantasy (Glorantha)
What you get A toolkit of rules to adapt Setting, scenarios, sanity rules, ready-to-play structure Setting, cultures, magic systems, ready-to-play structure
Best for Groups with their own setting or a genre the dedicated games don't cover Players who want investigation and dread out of the box Players who want a deep fantasy world
Prep burden Higher—you build the frame Lower—the frame is provided Lower—the frame is provided

The practical rule: choose BRP when the setting is yours; choose a Chaosium game when the setting is theirs. A group that wants to run a gritty modern espionage campaign or a homebrew sci-fi setting gets more from BRP than from bending Call of Cthulhu to fit. A group that wants to play investigators facing cosmic horror gets more from Call of Cthulhu, which packages the sanity mechanics and scenario support that BRP leaves you to assemble.

Deciding Whether BRP Is Right for You

BRP fits well if most of these are true:

  • You like percentile skills because players can read their odds directly off the sheet.
  • You want one ruleset for multiple campaigns instead of learning a new system per genre.
  • You're comfortable doing setting work—deciding what skills exist, what equipment costs, and what the tone is.
  • You prefer competence-and-attrition play over rapid power escalation; BRP characters tend to grow steadily rather than level up dramatically.

BRP is a weaker fit if you want a campaign handed to you with maps, factions, and a metaplot, or if your group expects character classes and levels as a familiar scaffold.

Getting Started

  1. Get the core BRP book and read the character creation and skill resolution chapters first—those two chapters carry most of the system.
  2. Pick a genre and write a one-paragraph setting brief (place, tone, what characters do). This is the step BRP expects you to do that dedicated games do for you.
  3. Decide which optional rules you'll use—the book presents modular options, and choosing up front prevents mid-session rules debates.
  4. Build characters together so the group agrees on which skills matter for your setting.
  5. Run a short scenario and check whether the graded-outcome rolls feel right for your table before committing to a long campaign.

Common sticking points: groups often skip the setting brief and then find skill lists don't match their genre; and newcomers sometimes treat special/critical results as optional flavor when they're central to how BRP combat and contests feel. Settle both before play.

For current BRP products and editions, check Chaosium's own catalog rather than relying on secondhand summaries, since the line is actively supported alongside Call of Cthulhu, RuneQuest, Pendragon, and 7th Sea.