The Landsknechte (singular: Landsknecht, pronounced [ˈlantsknɛçt]), also rendered as Landsknechts or Lansquenets, were German mercenaries used in pike and shot formations during the early modern period. Consisting predominantly of pikemen and supporting foot soldiers, their front line was formed by Doppelsöldner ("double-pay men") renowned for their use of Zweihänder and arquebus. They formed the bulk of the Holy Roman Empire's Imperial Army from the late 15th century to the early 17th century, fighting in the Habsburg-Valois wars, the Habsburg-Ottoman wars, and the European wars of religion.

Although prone to mutiny if unpaid and divided within their ranks between Catholics and Lutherans, the Landsknechte were well-armed and experienced warriors, recruitable in large numbers throughout Germany and Austria by the Holy Roman Emperor. This guaranteed both quantity and quality to the Imperial military for a century and a half. At their peak during the reign of Charles V of Habsburg, and under the leadership of notable captains such as Georg von Frundsberg and Nicholas of Salm, the Imperial Landsknechts obtained important successes such as the capture of the French King Francis I at the Battle of Pavia in 1525 and the resistance against the Ottoman Turks led by Suleiman the Magnificent at the Siege of Vienna in 1529, while also being responsible for the Sack of Rome in 1527.

The Germanic compound Landsknecht (earlier Lantknecht, without Fugen-"s") combines Land and Knecht to form "servant of the land". The compound Lantknecht was used during the 15th century for bailiffs or court ushers.

The word Landsknecht first appeared in the German language circa 1470 to describe certain troops in the army of Charles, Duke of Burgundy. As early as 1500, the term was morphed into Lanzknecht, referring to the unit's use of the pike as its main weapon.

Over the Burgundian Wars, the well-organized and supplied armies of Charles the Bold were defeated again and again by the Swiss Confederation, which wielded an ad hoc militia army. Charles's army lacked esprit de corps because of its composition by feudal lords, mercenaries, and levied gentry. The Swiss army, though poorly organized, were highly motivated, aggressive, and well-trained with their arms. The Swiss pikemen, called Reisläufer, repeatedly defeated and eventually killed Charles, eliminating Burgundy as a European power. Archduke Maximilian, who became co-ruler of Burgundian lands in 1477 by marrying Mary of Burgundy, was greatly influenced by the Swiss victories. When the French contested the inheritance, Maximilian levied a Flemish army and defeated the French in 1479 at the Battle of Guinegate, mixing Swiss-styled square infantry formation and Hussite wagon forts tactics. The dissolution of his levied army at war's end found Maximilian wanting a permanent and organized military force like the Confederation's to protect his domain. The existing Burgundian structure was inadequate to this end, however, and moreover the French wielded a monopoly on the hiring of Reisläufer.

Maximilian began raising the first Landsknecht units in 1486, amassing 6,000–8,000 mercenaries. One of these units he gave to Eitel Friedrich II, Count of Hohenzollern, who trained them with Swiss instructors in Bruges in 1487 to become the "Black Guard" – the first Landsknechte. In 1488, Maximilian organized the Swabian League, creating an army of 12,000 infantry and 1,200 cavalry to deter Bavaria and Bohemia. This is considered to be the first Landsknecht army to be raised in Germany. Maximilian raised a strong army for the Austrian-Hungarian War of 1490, and succeeded in driving the Hungarians out of Austria. The Landsknechte in his army refused to serve after sacking Stuhlweissenburg (now Székesfehérvár, Hungary), citing lack of pay and stopping Maximilian's advance on Buda. To prevent a repeat of Stuhlweissenburg, Maximilian now sought to homogenize the Landsknechte into a fully professional, and mostly Germanic military force.

In the 1490s, the well-trained Landsknechte managed to defeat significantly greater Frisian armies. Paul Dolnstein [de] wrote of the siege of Älvsborg Fortress in July 1502, fighting for the king of Denmark: "We were 1800 Germans, and we were attacked by 15000 Swedish farmers ... we struck most of them dead." After the Battle of Novara in 1513, the Swiss executed the hundreds of German Landsknecht mercenaries they had captured who had fought for the French. At the Battle of Bicocca and the Battle of Marignano (1515), the Landsknecht performed well, defeating the famed Reisläufer.

The Imperial Landsknechte were instrumental in many of the Emperor's victories, including the decisive Battle of Pavia in 1525. The same year, they also managed to defeat the peasants' revolt in the Empire. At their peak in the early 16th century, the Landsknechte were considered formidable soldiers who were often brave and loyal. However, these qualities may have declined afterward. The Landsknechte were also employed by the Habsburg emperor and the royal Valencian authorities in the suppression of the First Revolt of Espadà of 1526, which took place in the mountains of Espadà, in modern-day Spanish Castelló province (then in the Aragonese Kingdom of Valencia), where thousands of Valencian Muslim fellahs took up arms against the decree of forced conversion issued that very year by the emperor.