殿下，原指殿阶之下，后来成为中国对皇族成员的尊称，次于代表君主的陛下。汉朝开始称呼太子、诸王为殿下，三国开始皇太后、皇后也称殿下。唐代以后，惟太子、皇太后、皇后称“殿下”。

中国的藩属国的君主亦称殿下，如朝鲜王朝称自己的国王为殿下（朝鲜语：전하）、宗亲称呼君主为主上（朝鲜语：주상），王世子为邸下（朝鲜语：저하）。

日本称自己的包括三后（太皇太后、皇太后、皇后）的皇族还有摄政、关白、征夷大将军为殿下。明治维新后，亲王、内亲王、王、女王等皇族尊称为殿下，而皇后称陛下。

在欧洲国家，殿下相当于英语中的Your/His/Her (Imperial, Royal, Grand Ducal, Ducal Serene, Serene, Illustrious, etc.) Highness。

Highness is a formal style used to address (in second person) or refer to (in third person) certain members of a reigning or formerly reigning dynasty. It is typically used with a possessive adjective: "His Highness", "Their Highnesses", etc. Although often combined with other adjectives of honour indicating rank, such as "Imperial", "Royal" or "Serene", it may be used alone.