Spasticity is a frequent symptom in stroke, multiple sclerosis, cerebral or spinal trauma, and cerebral palsy that affects and disables a large number of adults and children. In this review, we discuss the pathophysiology and nonpharmacologic and pharmacologic treatments of spasticity with emphasis on the role of botulinum neurotoxins (BoNTs). The world literature is reviewed on double-blind and placebo-controlled clinical trials reporting safety and efficacy of BoNT treatment in adult spasticity and spasticity of children with cerebral palsy. The evidence for efficacy is presented from recommendations of the Assessment and Therapeutics subcommittee of the American Academy of Neurology. A technical section describes the techniques and recommended doses of BoNTs in spasticity.