Bovine spongiform encephalopathy (BSE) is a neurological disease condition in cattle that is thought to have originated in Great Britain. It occurs in cattle between two and eight years old and is always fatal. The most plausible cause of the disease is a prion, a "self-replicating" protein. BSE causes a portion of the brain to become sponge-like. Brain, central nervous system tissue, and the distal ileum (portion of the small intestine) can carry the infective agent, and measures have been taken to exclude those parts known to carry the infective agent (primarily brain and central nervous system tissue) from the food and feed supply.

BSE is similar to other transmissible spongiform encephalopathies (TSEs) present in humans and animals. In animals, the TSEs include scrapie (sheep and goats), chronic wasting disease (deer and elk), transmissible mink encephalopathy (mink), and feline spongiform encephalopathy (felines). In humans, Creutzfeldt-Jakob disease (CJD), variant-CJD (v-CJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), fatal familial insomnia (FFI), and Kuru are all transmissible spongiform encephalopathies.

BSE is thought to be linked to v-CJD. Pathological similarities exist between the two conditions, which has led scientists to speculate that the two conditions are related.