According to the International Association for the Study of Pain (IASP), pain is un unpleasant sensory and emotional experience signaling the presence of actual or potential tissue damage, or described in terms of such damage. Clinically, however, pain without proven evidence for its origin, should also be considered and treated nonetheless. Pain is classified as acute and chronic, or nociceptive and neuropathic pain. Acute pain is an adaptive, beneficial response which is necessary for the preservation of tissue integrity. When it becomes a chronic pain, which is a pain that has outlived its usefulness, it may be a timeless, endless, and meaningless perception, bringing the subject a sense of isolation and despair. Therefore, adequate management of pain is absolutely mandatory using whatever modalities. Nociceptive pain is initiated by noxious stimuli, whereas the neuropathic pain is induced by injury to either peripheral or central nervous system. If the pain is not treated or undertreated, noxious stimuli evoke long-term and persistent changes in the dorsal horn neurons in the spinal cord. These changes engrave the memory of the stimuli and sensitize the dorsal horn neurons. Subsequent pain stimuli evoke a even greater response, which results in a centrally mediated secondary hyperalgesia, and is mediated through glutamate acting on the N-methyl-diaspartate (NMDA) receptors. Mechanisms and pathophysiology of each pain are described briefly.