You and 3 others each start with 10 coins per round. Any coins you put into the shared pot get doubled and split equally among everyone — even those who contributed nothing. Will you cooperate, or keep your coins to yourself?
Round 1: How many coins will you contribute?
You have 10 coins. Slide to choose your contribution to the group pot.
No rounds played yet. Make your first contribution! 👆
If everyone contributes everything, the pot grows huge and everyone wins. But each person keeps more for themselves by contributing less — the temptation to free ride is what makes cooperation so hard.
The Public Goods Game models one of the trickiest problems in economics and society: how do groups fund things that benefit everyone, when any individual could benefit without paying? In this game, every player secretly decides how much of their own money to put into a shared pot. That pot is then multiplied — representing the extra value created when people work together — and the multiplied total is split equally among all players, no matter how much each person contributed.
Here's the catch: from a purely selfish, single-round perspective, the smartest move is to contribute nothing. You still get an equal share of whatever everyone else put in, but you keep all of your own coins too. This is called free riding. The problem is that if everyone reasons this way, nobody contributes, the pot stays small, and the whole group ends up worse off than if everyone had cooperated.
Researchers who study this game in real experiments find that people usually start out contributing a moderate amount — driven by fairness and optimism — but contributions tend to decline over repeated rounds as free riders take advantage and cooperators feel like suckers. This "decay of cooperation" is one of the most robust findings in behavioral economics, and it explains a lot about why real-world collective action — from climate change to community fundraising — is so difficult to sustain without rules, punishment, or trust.
The multiplier is the key ingredient that makes cooperation worthwhile in principle: because contributing money to the group *creates* more value than keeping it for yourself, society as a whole gains when people contribute. The challenge is making sure enough individuals believe others will also contribute so that cooperation doesn't collapse.
Gather 4 people and 10 tokens (coins, candy, or paper slips) each. Each round, everyone secretly decides how many tokens to put into a shared cup, then reveal at the same time. Double the pot and split it evenly. Play 5 rounds and track how contributions change over time — do they rise, fall, or stay steady? Then try adding a rule: publicly announce who contributed the least each round, and see if "peer pressure" changes behavior.
What is the Public Goods Game?
It's a game where each player decides how much of their own money to put into a shared pot. The pot is multiplied and then split equally among everyone, whether they contributed a lot or nothing at all.
What is free riding?
Free riding is when someone enjoys the benefits of a shared resource or group effort without contributing their fair share, relying on others to do the work.
Why do public goods games usually end with low contributions?
Because each individual keeps more money by contributing less, even though the group as a whole would be better off if everyone contributed a lot. This tension causes contributions to fall over repeated rounds.
Where do we see public goods problems in real life?
Paying taxes for roads and schools, reducing pollution to fight climate change, volunteering for community clean-ups, and contributing to open-source software are all real-world examples.