A sotnia (Ukrainian and Russian: сотня, lit. 'a hundred', Croatian: satnija) was a military unit and administrative division in some Slavic countries.

Sotnia, deriving back to 1248, has been used in a variety of contexts in both Ukraine and Russia to this day. It is a helpful word to create short names for groups including the Nebesna Sotnia and Terek Wolf Sotnia, stating that these groups do include 100–150 persons.

The military unit analog and most meaningful translation for the English-speaking world would be a company.

Its significance can be noticed by nationalist impact within the 16th-18th century Cossacks, Ukrainian People's Republic, Ukrainian National Army, and during Euromaidan.

Sotnia can also be referred to as half-sotnia which is a more diminutive unit of people. This typically consists of around 50 people.

In Russian history, sotnya (see Сотня) was also a unit of some other (civil) organizations, such as the Black Hundreds.

As a unit of the Cossack regiments, it is known from the earliest records of the Zaporizhian Sich.

During the Cossack service in the Imperial Russian Armies the typical regiment had five sotnias or squadrons. The term was used in the context of Cossack foot or cavalry regiments. The unit term was retained until the establishment of Soviet Union in 1922 and termination of the Ukrainian People's Republic and Free Don Cossack Oblast.