Paralysis is the complete loss of muscle function for one or more muscle groups, when the thing that is paralysed cannot move.

Paralysis is most often caused by damage to the nervous system or brain, especially the spinal cord. Major causes are stroke, trauma, poliomyelitis, amyotrophic lateral sclerosis (ALS), botulism, spina bifida, multiple sclerosis, and Guillain-Barré syndrome. Partial paralysis can also occur in the REM stage of sleep (see:Sleep paralysis). Paralysis often includes loss of feeling in the affected area.