In theoretical physics, a global anomaly is a type of anomaly: in this particular case, it is a quantum effect that invalidates a discrete symmetry that would otherwise be preserved in the classical theory.

Alternatively, the existence of a global anomaly implies that the measure of Feynman's functional integral cannot be defined globally.

The adjective "global" refers to the properties of a group that are not visible locally. For example, all features of a discrete group (as opposed to a Lie group) are global in character.

Many types of global anomalies must cancel for a theory to be consistent. An example is modular invariance, the requirement of anomaly cancellation for a part of a gravitational anomaly that deals with the large diffeomorphisms.