The 11th International Brigade, also called Thälmann or Thälmann Brigade, later called 11th Mixed Brigade, was the first of the International Brigades and was formally constituted on October 22, 1936. The Brigade was formed mostly by German and Austrian citizens, and it was completely reorganized in the spring of 1938. It participated in major battles of the Spanish Civil War, such as the Battle of Madrid and the Guadalajara Counterattack. In 1938, after the Battle of the Ebro, the brigade was completely reorganized as a mixed Spanish brigade, losing its international component, but still maintained a significant number of international brigadiers among its flanks until the end of the war.

The original units that formed the Brigade were the German Edgar André Battalion, the French Commune of Paris Battalion and the Italian Garibaldi Battalion, but along its existence passed a large number of battalions, from other brigades or new ones: the Dombrowski Battalion (Polish and Spanish), the Asturias-Heredia Battalion (Spanish), the Thälmann Battalion (German, Scandinavian and Spanish), the 6th of February (Six Fevrier) Battalion (Franco-Belgian), the 12th of February Battalion (Austrian and Spanish), the Dimitrov Battalion (Balkan), the Abraham Lincoln Battalion (US and Canadian) and the Hans Beimler Battalion (German, Dutch and Spanish).

The 11th Brigade was sent immediately to Madrid where it held positions in the University City and in the Casa del Campo. In the Battle of Madrid, the brigade was battered to the point of having to be relieved by the 12th International Brigade and taken to Archena to cover losses. On November 28, it returned to its old position but the Thälmann Battalion of the 12th International Brigade went to the 11th Brigade which in turn gave to the 12th Brigade the Garibaldi Battalion.

The brigade also participates in the First Battle in defense of the La Coruña road where it suffered heavy casualties, especially in the Thälmann Battalion. After a short break, it kept fighting without success for the disputed road, and human sacrifices were enormous. Losses caused by the continuous attacks forced the 11th Brigade to a new withdrawal to Murcia for its reorganization. On January 3, 1937, began the third attack against the Republican lines and the unit returned again to this sector. The battalions managed to contain the assault, but with the cost of heavy casualties.

In the Offensive of Jarama, while the Thälmann and the Paris Commune managed to hold their positions, the Edgar Andre disbanded which cost a lot of effort to regroup. During the Republican offensive on Brunete, the 11th Brigade suffered thousand casualties without achieving their goals and had to retire to Colmenarejo, Galapagar and Torrelodones to restore effective.

On August 19, it went to the front of Aragon to intervene in the Republican offensive against Zaragoza. The counterattack resulted in a failure and retreat to the trenches of the Masía del Chantre. From January 5 to 8, 1938, it acted in the area of La Muela de Teruel. Then, it went to Alfambra and to Singra to engage again to a bloody fight. The casualties suffered in these two stages were enormous.

During the offensive of Aragon, the brigade was defeated and it retreated hastily towards Albalate del Arzobispo and from there to the Sierra del Vizcuerno. The remains, approximately 80, were aimed at Cherta, where they crossed the Ebro.

The brigade was so shaken that it had to resort recruiting massive Spanish volunteers, so that for the Ebro Offensive, where it helped the 15th International Brigade in their desperate attempt to advance, because the Anglo-Saxon brigade had already lost many casualties, was practically a brigade formed by Spaniards and a few German, Austrians and Scandinavians.

On September 22, the Republican government decided to withdraw the International Brigades and it got called the 11th Mixed Brigade. On November 13, it was in reserve and covered the right flank of the retreats by the area of Ribarroja, crossing the Ebro. During the offensive in Catalonia, the brigade was virtually eradicated.