Belief revision is the process of changing beliefs to take into account a new piece of information. The logical formalization of belief revision is researched in philosophy, in databases, and in artificial intelligence for the design of rational agents.

What makes belief revision non-trivial is that several different ways for performing this operation may be possible. For example, if the current knowledge includes the three facts "${\displaystyle A}$ is true", "${\displaystyle B}$ is true" and "if ${\displaystyle A}$ and ${\displaystyle B}$ are true then ${\displaystyle C}$ is true", the introduction of the new information "${\displaystyle C}$ is false" can be done preserving consistency only by removing at least one of the three facts. In this case, there are at least three different ways for performing revision. In general, there may be several different ways for changing knowledge.