The criteria, key locations, classifications and functions of common neuro transmitters is reviewed and discussed. Neurotransmitters are the brain chemicals that communicate information throughout our brain and body. They relay signals between neurons. To be neurotransmitter the molecule must be present in the brain and distributed unevenly and enzymes that help to create the neurotransmitter must be present in the brain. Common inhibitory neurotransmitters such as serotonin, Gamma-amino butyric acid (GABA) and dopamine calm the brain and help create balance where as excitatory neurotransmitters such as norepinephrine, glutamate, epinephrine, and dopamine stimulate the brain. From inhibitory neurotransmitters dopamine is located in Amygdala, Cingulate cortex, Hippocampus, Nucleus... accumbens. Olfactory bulb, Prefrontal cortex, substancia nigra and hypothalamus and it is mainly involved in movements, emotions, sexual arousal and cognitive functions where as Serotonin is located in Amygdala, Cingulate cortex, Hippocampus, thalamus, septum, neocortex, ventral tagemental area and hypothalamus and it is mainly involved in emotions, sleep, body temperature regulation and pain suppressions. From excitatory neurotransmitters norepinephrine is found in Amygdala, Hippocampus, brainstem, Spinal cord, Cerebellum, Cerebral cortex, Hypothalamus, Tectum, Thalamus, Ventral tegmental area, and Olfactory bulb and mainly involved in anxiety, mood, sympathetic arousal, cognitive control, working memory, hunger and circadian rhythm. Acetylcholine is found nucleus basalis of meynert, medial septal nucleus, diagonal band hippocampus, Cerebral cortex, limbic cortex, sensory cortex, thalamus and Ventral tegmental area and mainly involved in emotions, wakefulness and attention (arousal), short term memory, learning and motor functions.