Registered Cossacks
| Zaporozhian Host | |
|---|---|
| Active | 1572–1699 |
| Country | Polish–Lithuanian Commonwealth |
| Allegiance | Polish–Lithuanian Commonwealth |
| Branch | Army |
| Type | Light cavalry Skirmisher |
| Role | Patrolling Raiding Reconnaissance Screening Shock tactics Wagon fort |
| Size | up to 40,000 (1649) |
| Garrison/HQ | Trechtymirów (Trakhtemyriv), Kiev Voivodeship |
| Engagements | Livonian War, Moldavian Magnate Wars, Polish–Ottoman War, Polish–Muscovite War |
| Commanders | |
| Notable commanders | Petro Konashevych-Sahaidachny, Mykhailo Doroshenko, others |
Registered Cossacks (Ukrainian: Реєстрові козаки, romanized: Reiestrovi kozaky; Polish: Kozacy rejestrowi) comprised special Cossack units of the Polish–Lithuanian Commonwealth army in the 16th and 17th centuries.
Registered Cossacks became a military formation of the Commonwealth army beginning in 1572 soon after the Union of Lublin (1569), when most of the territory of modern Ukraine passed to the Crown of Poland. Registered Cossack formations were based on the Zaporozhian Cossacks who already lived on the lower reaches of the Dnieper River amidst the Pontic steppes as well as on self-defense formations within settlements in the region of modern Central and Southern Ukraine.
Following the Khmelnytsky Uprising of 1648 the majority of Registered Cossacks joined the rebels, contributing to the Polish defeat. The term "Registered Cossacks" largely went out of use after the 1660s, as various Cossack troops were integrated into the military of the Cossack Hetmanate, a vassal state of the Tsardom of Russia and, later, the Russian Empire.