The republics were established in early Soviet Russia after the collapse of the Russian Empire.
The Federation of Russia is divided into 85 constituent units known as federal subjects. Of the 85 federal subjects, 21 are republics (22 if Crimea is included).
Most of the republics represent areas of non-Russian ethnicity, although there are several republics with Russian majority. The indigenous ethnic group of a republic that gives it its name is referred to as the "titular nationality".
They can also be called states inside the state, as they have their own constitutions and legislature (the Russian constitution still has an upper hand in resolving conflicting issues).