A Regimentarz (from Latin: regimentum) was a military commander in Poland, since the 16th century, of an army group or a substitute of a Hetman. He was nominated by the King of Poland or the Sejm. In the 17th century a Regimentarz was also the commander of Pospolite ruszenie in cases where a castellan or a voivode could not command personally. Regimentarz generalny was the commander of Confederations.