Abstract: Chemical neurotransmission is mediated by specific neurotransmitters in the brain, and a large number of these have been identified. There are various classes of neurotransmitters in the central nervous system. Amine and monoamines are of special interest in our discussion and are reviewed here. Other classes of neurotransmitters, not reviewed here, use different pathways for synthesis, storage, release, and ways of communication. Still others follow non-synaptic neurotransmission. Major neurotransmission systems of interest reviewed here are cholinergic system, dopaminergic system, GABAergic system, glutamatergic system, noradrenergic system, and serotonergic system. Pharmacodynamics comprises the concepts of drug sites of action, the structure activity relationship, specific receptors, the drug-receptor interactions, and mechanisms of drug action. These concepts are reviewed here in the context of chemical neurotransmission.