You start each round with 10 coins. Whatever you send to your partner triples in value — but it's up to them how much they send back. Will trusting them pay off?
Round 1: How much will you send Tala?
Whatever you send gets tripled before Tala decides what to return.
No rounds played yet. Send your first coins! 👆
If you send everything and they return half, you both end up richer than if you sent nothing. Trust creates value — but sending money is a real risk if your partner turns out to be selfish.
The Trust Game, sometimes called the Investment Game, is a classic experiment in behavioral economics designed to measure trust and trustworthiness. One player, the sender, decides how much of their money to send to a second player, the trustee. That amount is multiplied — usually tripled — representing how trust and cooperation can create new value, much like an investment growing over time. The trustee then decides how much of that larger amount to send back to the sender, keeping the rest.
A purely selfish trustee would keep everything and send nothing back, since there's no further round to punish them. Knowing this, a purely selfish sender should therefore send nothing at all in a one-shot game. But real people rarely play this way. In actual experiments, senders typically send around half their money, and trustees often return a meaningful share, driven by fairness, gratitude, or guilt at betraying someone's trust.
This game beautifully illustrates the gap between "rational" self-interest and how humans actually behave. It also shows why trust is so valuable: because the total amount of money in the game grows every time it's sent, both players can end up richer than they started — but only if the sender is willing to take a risk and the trustee is willing to reciprocate.
Playing multiple rounds against the same partner adds a new dimension: reputation. If a trustee returns generously in early rounds, senders learn to trust them more and send larger amounts, creating a virtuous cycle of growing cooperation. If a trustee betrays that trust even once, senders often pull back sharply, showing how fragile trust can be compared to how slowly it's built.
Pair up with a partner and give each person 10 tokens. The sender picks an amount to give, which you triple using extra tokens from a shared bank. The trustee then decides how many tokens to give back. Play 3 rounds, switching who is the sender each time. Compare how much everyone sent and returned, and discuss whether trust grew or shrank as the rounds went on.
What is the Trust Game?
The Trust Game has two roles: a sender who decides how much money to send, which triples in value, and a trustee who decides how much of that tripled amount to send back to the sender.
Why does the money triple?
The tripling represents the extra value created by trust and cooperation, similar to how investing money or working together can create more value than keeping resources separate.
What does the game reveal about human behavior?
Most people send and return more than a purely selfish strategy would predict, showing that real people care about fairness and reciprocity, not just maximizing their own money.
How is the Trust Game used in real research?
Economists and psychologists use it to measure trust and trustworthiness across different cultures, ages, and relationships, and to study how trust builds or breaks down over repeated interactions.