Spasticity is an abnormal increase in muscle contraction often caused by damage to central motor pathways that control voluntary movement. During clinical examination, spasticity manifests as an increase in stretch reflexes, producing tendon jerks and resistance appearing as muscle tone. There are many causes of spasticity, including demyelination from multiple sclerosis, congenital damage from diseases such as cerebral palsy, trauma to the brain or spinal cord, hemorrhage or infarction, and other pathologic conditions that interrupt neural pathways. Effects of spasticity range from mild muscle stiffness to severe, painful muscle contractures and repetitive spasms that reduce mobility and substantially impede normal activities of daily living. Botulinum toxin therapy reduces spasticity and pain associated with several disorders. Local treatment with botulinum toxins can be used as adjunctive therapy, along with oral antispasticity medications, or alone to provide localized decrease in symptoms of spasticity and pain. Botulinum toxin therapy may be particularly useful for patients with spasticity due to stroke, whose treatment can be tailored based on recovery of function over time. In addition, botulinum toxin therapy is safe for pediatric patients, including children with cerebral palsy, who may not be able to tolerate the cognitive side effects of oral medications. Results of studies evaluating botulinum toxin for the treatment of spasticity due to various causes are presented here.