Botulinum toxins are among the most potent neurotoxins known to humans. In the past 25 years, botulinum toxin has emerged as both a potential weapon of bioterrorism and as a powerful therapeutic agent, with growing applications in neurological and non-neurological disease. Botulinum toxin is unique in its ability to target peripheral cholinergic neurons, preventing the release of acetylcholine through the enzymatic cleavage of proteins involved in membrane fusion, without prominent central nervous system effects. There are seven serotypes of the toxin, each with a specific activity at the molecular level. Currently, serotypes A (in two preparations) and B are available for clinical use, and have been shown to be safe and effective for the treatment of dystonia, spasticity, and other disorders in which muscle overactivity gives rise to symptoms. This review focuses on the pharmacology, electrophysiology, immunology, and application of botulinum toxin in selected neurological disorders.