What is Call of Cthulhu?

Call of Cthulhu (CoC) is a horror tabletop RPG based on H.P. Lovecraft’s mythos of cosmic dread. First published in 1981 by Chaosium, it uses the Basic Role-Playing (BRP) system — a percentile-based ruleset where skills are rated as percentages and you roll under your skill on d100 to succeed.

Unlike most RPGs where characters grow more powerful, Call of Cthulhu investigators are ordinary people — professors, journalists, detectives, war veterans — who stumble into horrors beyond human comprehension. The question isn’t whether you can win, but whether you’ll survive with your sanity intact.

The Horror of CoC

Call of Cthulhu is built on the philosophy of cosmic horror: the idea that the universe is vast, indifferent, and populated by entities so alien that merely understanding them can shatter the human mind. You’re not a hero. You’re an ant that’s noticed the boot.

Investigations drive the gameplay. Players gather clues, interview witnesses, research forbidden texts, and piece together the nature of the threat. Combat is dangerous and often a last resort — most monsters cannot be fought with a pistol and hope.

Why Play Call of Cthulhu?

• Unique tone: No other RPG captures the feeling of creeping dread and existential horror like CoC. It’s a completely different experience from fantasy adventuring.
• Investigation-focused: If you love mysteries, research, and piecing together clues, CoC is the ultimate investigative RPG.
• SAN mechanics: The Sanity (SAN) system mechanically represents psychological trauma — losing points as you encounter the unknowable.
• Flexible time periods: Default is 1920s, but official supplements cover the 1890s, modern day, the future, and even ancient Rome.

Core Mechanics

CoC uses percentile dice (d100). Each skill has a rating (e.g., Library Use 75%). You roll d100 and try to get under your skill. Rolling under half your skill is a “special success” with extra benefits. Rolling 96-100 is always a failure — and often a spectacular one.

Sanity points are a core resource. Encountering horrors costs SAN. Losing too much leads to temporary or permanent insanity. The Keeper (GM) tracks SAN loss carefully — it’s the game’s most important mechanic.

What You Need to Play

• Call of Cthulhu Keeper Rulebook — Core rules for GMs and players ($40-50)
• Percentile dice — Two d10s (one for tens, one for ones) or a dedicated d100
• Character sheet — Included in the rulebook, also free online
• A Keeper — The GM in CoC, who guards the secrets of the mythos
• Scenario — “The Haunting” (included in starter set) is the classic first adventure

Iconic Scenarios

CoC has some of the most celebrated scenarios in RPG history. Masks of Nyarlathotep is the legendary globe-spanning campaign. Horror on the Orient Express is a classic mystery. Dead Light is a perfect one-shot. The 7th edition Starter Set includes several excellent scenarios for new groups.