Military of the Polish–Lithuanian Commonwealth

The military of the Polish–Lithuanian Commonwealth consisted of two separate armies of the Kingdom of Poland's Crown Army and the Grand Duchy of Lithuania's Grand Ducal Lithuanian Army following the 1569 Union of Lublin, which joined to form the bi-conderate elective monarchy of the Polish–Lithuanian Commonwealth. The army of each country was commanded by their respective Hetmans. A distinctive formation of both armies were the Winged hussars. The Polish–Lithuanian Commonwealth Navy never played a major role and ceased to exist in 1643.

Commonwealth forces were engaged in numerous conflicts in the south (against the Ottoman Empire), the east (against the Tsardom of Muscovy and later, the Russian Empire) and the north (the Kingdom of Sweden); as well as internal conflicts (most notably, numerous Cossack uprisings). For the first century or so, the Commonwealth military was usually successful, but became less so from around the mid-17th century. Plagued by insufficient funds, it found itself increasingly hard-pressed to defend the country, and inferior in numbers to the growing armies of the Commonwealth's neighbors.

Following the Commonwealth's end, the Commonwealth military traditions would be continued by Napoleonic Polish Legions and the Army of the Duchy of Warsaw.