Botulinum toxins are protein complexes comprised of a neuroactive protein, botulinum neurotoxin (BoNT), and several non-toxic associated proteins. All medical indications for botulinum toxins are based on the very long-term inhibitory action of BoNT on the release of neurotransmitter. BoNT is a 150 kDa protein that binds to nerve endings, is internalized in them and blocks the vesicular neurotransmitter exocytosis machinery. Depending on its serotype, BoNT cleaves one among the three SNARE proteins involved in the fusion of synaptic vesicles with the plasma membrane of nerve endings, regardless of the type of transmitter they contain. The very high selectivity of action of BoNT for neuron nerve terminals is mainly due to its binding a protein receptor (synaptotagmin or SV2, depending on the BoNT serotype), which is a synaptic vesicle membrane protein exposed on the surface of neuron terminations during neurotransmitter exocytosis. BoNT cannot cross the blood-brain barrier, therefore, its effects are mainly peripheral. Nevertheless, after an injection of BoNT in the periphery, the neurotoxin captured by the peripheral nerve endings can be retrogradely transported inside sensory neurons where it can act, thereby modifying sensory information ascending to the central nervous system. The neuronal specificity of BoNT makes it a therapeutic tool used in a wide range of indications in physical and rehabilitation medicine, neurology, ophthalmology, urology and pain management.