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Game Theory · Microeconomics · ~5 min
Prisoner's Dilemma
Two suspects, two locked rooms, one deal each. Cooperate with your partner and stay silent — or defect and rat them out. Play a round or an iterated series against classic strategies from Axelrod's 1980 tournament.
The payoff matrix
Years in prison. Lower is better. Your outcome is the first number in each cell.
They cooperate
They defect
You cooperate
3, 3Both stay quiet — light sentence
0, 5You're stuck — they walk free
You defect
5, 0You walk free — they're stuck
1, 1Mutual betrayal — hard time both
Scoring: cooperate–cooperate = 3 each. Defect against cooperator = 5. Get defected on while cooperating = 0. Mutual defection = 1. Total is what you keep.
Round 1 of 10
vs. Tit-for-Tat
Make your choice. Your opponent chooses at the same time — no peeking.
Your history
Their history
Why this game matters
The Prisoner's Dilemma is the sharpest illustration of a problem that runs through economics, politics, and biology: what's rational for each person alone can be worse for everyone together. Defection is the dominant strategy in one round — no matter what your partner does, you're better off defecting. But if both of you reason that way, you both get 1 instead of 3.
Robert Axelrod's 1980 computer tournament found that Tit-for-Tat — the simplest possible cooperative strategy — beat every complex algorithm submitted. It was nice (cooperated first), provocable (retaliated immediately), forgiving (returned to cooperation the moment the other side did), and clear. Those four properties turn out to be a recipe for cooperation in worlds without contracts.
The same math describes cartels, arms races, climate treaties, and why your roommate does the dishes. Play a few matches and notice: your strategy against Always-Defect and against Tit-for-Tat should be very different.