In religion, the Slavs traditionally divided into two main groups: those associated with the Eastern Orthodox church (Russians, most Ukrainians, some Belarusians, Serbs, and Macedonians) and those associated with the Roman Catholic church (Poles, Czechs, Slovaks, Croats, Slovenes, some Ukrainians, and most Belarusians). The division is further marked by the use of the Cyrillic alphabet by the former (but including all Ukrainians and Belarusians) and the Latin alphabet by the latter. There are also many minority religious groups, such as Muslims, Protestants, and Jews; and in recent times Communist governments' official encouragement of atheism, together with a general trend toward secularism, has eroded membership in the traditional faiths.

Prehistorically, the original habitat of the Slavs was Asia, from which they migrated in the 3rd or 2nd millennium BC to populate parts of eastern Europe. Subsequently, these European lands of the Slavs were crossed or settled by many peoples forced by economic conditions to migrate. In the middle of the 1st millennium BC, Celtic tribes settled along the upper Oder River, and Germanic tribes settled on the lower Vistula and lower Oder rivers, usually without displacing the Slavs there. Finally, the movement westward of the Germans in the 5th and 6th centuries AD started the great migration of the Slavs, who proceeded in the Germans' wake westward into the country between the Oder and the Elbe-Saale line, southward into Bohemia, Moravia, Hungary, and the Balkans, and northward along the upper Dnieper River. When the migratory movements had ended, there appeared among the Slavs the first rudiments of state organizations, each headed by a prince with a treasury and defense force, and the beginning of class differentiation.

In the centuries that followed, there developed scarcely any unity among the various Slavic peoples. The cultural and political life of the west Slavs was integrated into the general European pattern. They were influenced largely by philosophical, political, and economic changes in the West, such as feudalism, Humanism, the Renaissance, the Reformation, and the French and Industrial revolutions. As their lands were invaded by Mongols and Turks, however, the Russians and Balkan Slavs remained for centuries without any close contact with the European community; they evolved a system of bureaucratic autocracy and militarism that tended to retard the development of urban middle classes and to prolong the conditions of serfdom. The state's supremacy over the individual tended to become more firmly rooted.

A faint kind of Slavic unity sometimes appeared. In the 19th century, Pan-Slavism developed as a movement among intellectuals, scholars, and poets, but it rarely influenced practical politics. The various Slavic nationalities conducted their policies in accordance with what they regarded as their national interests, and these policies were as often bitterly hostile toward other Slavic peoples as they were friendly toward non-Slavs. Even political unions of the 20th century, such as that of Yugoslavia, were not always matched by feelings of ethnic or cultural accord; nor did the sharing of communism after World War II necessarily provide more than a high-level political and economic alliance.