Botulinum neurotoxin (BoNT) is an effective treatment for conditions associated with overactivity of glandular, smooth or skeletal muscle, and this toxin can also ameliorate certain painful conditions. Electromyography, endoscopy and imaging techniques such as ultrasonography and fluoroscopy have been used to increase the accuracy of BoNT injections. This Review assesses the mechanisms of action of BoNT, and examines the use of BoNT injections in numerous neurological conditions, including dystonia, spasticity, headaches and other painful disorders, hemifacial spasm, essential tremor, motor tics, hyperhidrosis, and sialorrhea and drooling. Important practical aspects, such as the reconstitution of BoNT, dosing, and methods of administration, are also addressed.