Lisowczyks or Lisowczycy (Polish pronunciation: [lisɔfˈt͡ʂɨt͡sɨ]; also known as Straceńcy ('lost men' or 'forlorn hope') or chorągiew elearska (company of elears [pl]); or in singular form: Lisowczyk or elear) was the name of an early 17th-century irregular unit of the Polish–Lithuanian light cavalry. The Lisowczycy took part in many battles across Europe and the historical accounts of the period characterized them as extremely agile, warlike, and bloodthirsty. Their numbers varied with time, from a few hundred to several thousand.

The origin of the group can be traced to konfederacja (a form of semi-legal mutiny of royal forces, practiced in the Kingdom of Poland and then in the Commonwealth), organized around 1604 by Aleksander Józef Lisowski. They began to grow in strength and fame a few years later, when Lisowski's irregulars were incorporated into the forces fighting in Muscovy. The Lisowczycy unit of the Polish cavalry received no formal wages; instead, they were allowed to loot and plunder as they pleased. They relied on their speed and fought without tabors, foraging supplies from lands they moved through. The Lisowczycy were feared and despised by civilians wherever they passed and they gained dubious fame for the scores of atrocities they carried out (pillage, rape, murder and other outrages). However, they were also grudgingly respected by their opponents for their military skills. They did not hesitate to plunder even their homeland, where they sacked the Racovian Academy university of the Polish brethren. Such actions were among the reasons the Commonwealth ruler Sigismund III Vasa tried to keep them away from the Commonwealth for as long as possible.

The Lisowczycy took part in many conflicts, including the Dymitriads (where their actions help explain the text of the infamous placard in Zagorsk: three plagues: typhus, Tatars, and Poles), at the Battle of Humenné (where they prevented a Transylvanian army from laying siege to Vienna) and in the Battle of White Mountain (where they participated in Bohemia's defeat). They were eventually disbanded in 1635.

An account of Lisowczycy's exploits was written by their chaplain, Wojciech Dembołęcki (or Wojciech Debolecki), in Przewagi Elearów polskich co ich niegdy Lisowczykami zwano (1619–1623) (Deeds of Polish Elears once known as Lisowczycy (1619–1623)).

In 1604, during the early stages of the Polish–Swedish War, the Sejm of the Commonwealth failed to gather the money to pay its soldiers fighting in Livonia against the Swedes. Aleksander Józef Lisowski became one of the leaders of the resulting konfederacja – a section of the army that mutinied and decided to gather its outstanding wages by pillaging local civilians, not caring whether these owed their allegiance to the Commonwealth or to Sweden. Although this annoyed Great Hetman of Lithuania Jan Karol Chodkiewicz, and resulted in Lisowski being banished from the Commonwealth, little was done to stop the mutineers. Soon after, Lisowski with his followers joined the Sandomierz rebellion or rokosz of Zebrzydowski, a revolt against the absolutist tendencies of the King Sigismund III Vasa.

Eventually, after the rebel forces were defeated at the Battle of Guzow, Lisowski's fortunes turned for the worse and he became persona non grata in most of the Commonwealth, and was forced to seek refuge with the powerful Radziwiłł family. In the meantime, Muscovy's Time of Troubles were brewing, and Lisowski did not pass over the opportunity of profiting from this, as many other local magnates and noblemen already had, by meddling in Russian affairs. He soon decided he could profit best by lending his support to the Muscovite pretender, False Dmitriy II.

In 1608, together with Aleksander Kleczkowski, leading his forces – a band of few hundred ragtag soldiers of fortune, mainly Poles but also Lithuanians, and Ruthenians – he defeated the armies of tsar Vasili Shuisky, led by Zakhary Lyapunov and Ivan Khovansky, near Zaraysk and captured Mikhailov and Kolomna, moving on to blockade Moscow. However, he was soon to be defeated at Miedźwiedzi Bród, losing most of his loot. He reorganized the army and joined with Jan Piotr Sapieha, but they failed to capture the Troitse-Sergieva Lavra fortress and were forced to retreat to near Rakhmantsevo. Then came successful pillages at Kostroma, Soligalich, and some other cities (those battles took place around 1608–09). He took Pskov in 1610 and clashed with Swedes operating in Muscovy during the Ingrian War. The Lisowczycy proved essential in the defence of Smolensk in 1612, when most of the Commonwealth regular army, the (wojsko kwarciane), mutined and joined the Rohatyn Confederation. For the next three years Lisowski's forces were of importance in the guarding of the Commonwealth border against Muscovy incursions. In 1615, Lisowski gathered many outlaws and invaded Muscovy with six companies of cavalry. He besieged Bryansk and defeated the Muscovite relief force of a few thousand soldiers under Kniaz Yuri Shakhovskoy near Karachev. Lisowski moved on to defeat the Muscovite advance guard of a force (several times larger than his) under the command of Kniaz Dmitry Pozharsky, who decided not to attack and fortified his forces inside a camp. Lisowski's men broke contact with other forces, burned Belyov and Likhvin, took Peremyshl, turned north, defeated a Muscovite army at Rzhev, turned towards the Kara Sea coast, then to Kashin, burned Torzhok, returned to Commonwealth without any further contact with Muscovy forces. Until the autumn of 1616, Lisowski and his forces remained on the Commonwealth-Muscovy border, when Lisowski suddenly fell ill and died on October 11.

In 1612, when the Polish occupation of the Moscow Kremlin had ended (see Polish–Muscovite War (1605–18)), loose Polish forces, which had fought under Lisowski, scattered over vast territory of the Tsardom of Russia, taking advantage of the so-called Time of Troubles. Exact whereabouts of Aleksander Jozef Lisowski at that time are unknown: the legendary leader most likely roamed across northern Russia, together with his men.