Pain is one of the most common causes of suffering. The physiological function of pain is to alert the body of potentially noxious conditions encountered from the external or internal environment. Pain can be differentiated into acute pain and chronic pain according to its duration, with 3 months as a tentative defining point in humans. Acute pain is good for protection from dangerous health issues and relatively easy to control. Chronic pain, on the other hand, is absolutely annoying and notoriously difficult to manage. Chronic pain can be induced by various causes, such as inflammatory or metabolic disorders of the peripheral tissue, musculoskeletal strain, peripheral or central nervous lesion and diseases, etc., yet their common mechanism is hypersensitivity of the pain transmission and perception systems, which may result in a structural disorganization. The suffering from chronic pain has been a powerful driving force for pain research both in academic institutions and in the industry. This chapter focuses on the system of noxious signal transmission, from the ion channel and nociceptor to the psychological reaction, from the ascending pain perception pathways to the descending pain modulatory pathways, being facilitatory or inhibitory. Principles of biomedical interventions on acute and chronic pain are also outlined.