©　2013　Springer　Science+Business　Media,　LLC.　All　rights　are　reserved.　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.