Kohtla-Järve is a city and municipality in north-eastern Estonia, founded in 1924 and incorporated as a town in 1946. The city is highly industrial, and is both a processor of oil shales and is a large producer of various petroleum products. The city is also very diverse ethnically: it contains people of over 40 ethnic groups and only 21% of the population are Estonians. Many ethnic Estonians in the city have adopted Russian as their primary language, although this changed in the late 1990s, as Estonian once again became the primary language used in everyday life. Kohtla-Järve is the 4th largest city in Estonia.
The history of Kohtla-Järve is closely tied to the history of extraction of oil shale - the main mineral of Estonia. There is evidence that a number of settlements existed on the territory of modern Kohtla-Järve since the High Middle Ages. In the Danish Land Book, Järve and Kukruse villages were first mentioned in 1241 by the names Jeruius and Kukarus respectively, and Sompa village in 1420 by the name Soenpe.