Slavs
Slavs can be further grouped by religion. Orthodox Christianity is practiced by the majority of Slavs. The Orthodox Slavs include the Belarusians, Bulgarians, Macedonians, Montenegrins, Russians, Serbs, and Ukrainians and are defined by Orthodox customs and Cyrillic script as well as their cultural connection to the Byzantine Empire (Serbs also use Latin script on equal terms). Their second most common religion is Roman Catholicism. The Catholic Slavs include Croats, Czechs, Kashubs, Moravians, Poles, Silesians, Slovaks, Slovenes, and Sorbs and are defined by their Latinate influence and heritage and connection to Western Europe. There are also substantial Protestant and Lutheran minorities especially amongst the West Slavs, such as the historical Bohemian (Czech) Hussites.
Church Slavonic language
Church Slavonic, also known as Church Slavic, New Church Slavonic, or New Church Slavic, is the conservative Slavic liturgical language used by the Orthodox Church in Bulgaria, Poland, the Czech Republic and Slovakia, Russia, Belarus, Serbia, Montenegro, Bosnia and Herzegovina, the Republic of Macedonia, Ukraine, Slovenia, and Croatia. The language appears also in the services of the American Carpatho-Russian Orthodox Diocese and occasionally in the services of the Orthodox Church in America. It was also used by the Orthodox Churches in Romanian lands until the late 17th and early 18th centuries, as well as by Roman Catholic Croats in the Early Middle Ages.
It is also co-used by Greek Catholic Churches, which are under Roman communion, in Slavic countries, for example the Croatian, Slovak and Ruthenian Greek Catholics, as well as by the Roman Catholic Church (Croatian and Czech recensions, see below).