Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field.

The magnetoresistance of conventional materials enables changes in resistance of up to 5%, but materials featuring CMR may demonstrate resistance changes by orders of magnitude.

Initially discovered in 1993, this property is not explained by any current physical theories, including conventional magnetoresistance or the double-exchange mechanism . It is the focus of a great deal of ongoing research.

The understanding and application of CMR offers tremendous opportunties for the development of new technologies such as read/write heads for high-capacity magnetic storage and spintronics.