Diazepam is mainly used to relieve anxiety and to control agitation caused by alcohol withdrawal. It is also used along with other medications to control muscle spasms and spasticity caused by certain neurological disorders such as MS, cerebral palsy (condition that causes difficulty with movement and balance), paraplegia (inability to move parts of the body), athetosis (abnormal muscle contractions), and stiff-man syndrome (a rare disorder with muscle rigidity and stiffness). Diazepam is also used along with other medications to control seizures. Diazepam is in a class of medications called benzodiazepines. It works by calming abnormal overactivity in the brain.
Summary from MedlinePlus.gov, click for more information.