Cuirassiers were mounted soldiers with firearms originating in 16th-century Europe. In hindsight, they were a transitional form of cavalry unit between medieval armored knights and latter-day cavalry. The name comes from cuirass, the breastplate armor they used.

The first cuirassiers did not appear very different from the medieval knights; they wore full-body armor and the only things that separated them from the knight were riding boots and the use of wheel-lock pistol s, in addition to lances and swords.

Cuirassiers wore armor long after it had become superfluous in the face of ever increasing firearm use. However, the size of the armor gradually decreased so that, by the end of the 17th century, it contained only a breastplate (the cuirass), backplate, and helmet.

The first recorded cuirassiers were 100-man strong regiments of Austrian kyrissers that was formed in 1484 to serve the Holy Roman Emperor Maximilian . The French military introduced their own cuirassiers in 1666. By 1705, the Holy Roman Emperor's personal forces in Austria had twenty cuirassier regiments. Imperial Russia formed their own cuirassier regiments in 1732, including a guards regiment. The Russian cuirassier forces took part in the war against Turkey in 1736.

Cuirassiers were prominent in the armies of Frederick the Great of Prussia and Napoleon of France. The latter increased the amount of cuirassier regiments to 14 by the end of his reign.

Eventually most cuirassier regiments were turned into other forms of cavalry such as lancers, hussars, or particularly dragoons which were essentially mounted modern infantry. Some cavalry regiments use cuirasses as part of their parade paraphernalia and in other formal functions. The term cuirassiers has become mainly an honorific term retained from the regiment's past, if it is retained at all.