What Is Bayesian Game Theory?


Diego Sanchez

Bayesian game theory is a branch of game theory that deals with situations where players have incomplete information about their opponents. In such scenarios, players must make decisions based on their beliefs about the probability of different outcomes. This theory is particularly useful in situations where players must make decisions before knowing what their opponents will do.

How Does Bayesian Game Theory Work?

In a Bayesian game, each player has a set of possible types that determine their preferences over outcomes. A type can be thought of as a player’s private information, such as their skill level or risk aversion. Players do not know each other’s types, but they do have beliefs about the probability distribution over types.

Prior Beliefs

Before the game begins, each player has a prior belief about the distribution over types. This belief is represented by a probability distribution function (PDF), which assigns probabilities to each possible type.

Conditional Beliefs

As the game progresses and players observe their opponents’ actions, they update their beliefs about the distribution over types. These updated beliefs are called conditional beliefs and are represented by a new PDF.

Applications of Bayesian Game Theory

Bayesian game theory has many applications in economics, politics, and other fields. For example, it can help us understand how firms compete in markets where there is uncertainty about consumer demand or how politicians strategize during elections when there is uncertainty about voters’ preferences.

Auction Theory

One area where Bayesian game theory has been particularly useful is auction theory. Auctions involve multiple bidders who have incomplete information about each other’s valuations for an item being sold. By using Bayesian game theory, we can model how bidders update their valuations based on the actions of others and analyze how different auction formats affect the outcome.

Industrial Organization

Bayesian game theory has also been applied to industrial organization, the study of how firms compete in markets. By modeling firms’ beliefs about their competitors’ actions, we can analyze how different market structures affect competition and welfare.


Bayesian game theory is a powerful tool that allows us to analyze strategic interactions in situations where players have incomplete information. By modeling players’ beliefs about the probability of different outcomes, we can gain insights into how they make decisions and how different factors affect the outcome. This makes it an essential tool for economists, political scientists, and other social scientists who study strategic interactions.