上尉是军队的职衔，在少校和中尉之间。在少数国家，存在大尉军衔，作为上尉的更高一级军衔。在英文中，陆军以及由陆军衍生出来的军种（空军、陆战队）的上尉称为Captain，海军上尉称为Lieutenant。英国空军上尉则称为Flight Lieutenant。日本自卫队相当于上尉的阶级简称「1尉」，依军种分为「1等陆尉」、「1等海尉」及「1等空尉」，**的上尉军阶则称做「대위」（对应汉字为大尉）。

****上尉主要担任连长或副连长的职务，但可占缺担任辅导长。

英国陆军上尉主要担任副连长的职务，美国陆军上尉则担任连长的职务 。*****上尉则根据条例，可以担任从副连职军官、正连职军官和副营职军官。

Hauptmann is a German word usually translated as captain when it is used as an officer's rank in the German, Austrian and Swiss armies. While "haupt" in contemporary German means "main", it also has the meaning of "head", i.e. Hauptmann literally translates to "head man", which is also the etymological root of "captain" (from Latin caput head). It equates to Captain in the British and US Armies, and is rated OF-2 in NATO.