Meditation is a complex mental process that involves changes in cognition, sensory perception, emotions, hormones, and autonomic activity. Many different neurotransmitter systems, including dopamine, serotonin, glutamate, and opiates are likely affected by meditation practices. Meditation has also become widely used, either alone or combined with other therapies, for stress reduction, as well as for a variety of physical and mental disorders. There has been an increasing understanding of the overall biological mechanism of meditation practices in terms of their effects on the brain and the body. Recent studies using clinical tools and functional neuroimaging have substantially augmented knowledge of the biology of meditative practices.