The process of Immigration of ethnic non-Bulgarians to Bulgaria can be considered after the country's liberation from Ottoman rule and the restoration of the Bulgarian state in 1878. Following the Berlin Congress, the Russian Empire was forced to withdraw its troops from Bulgaria, but left a large number of specialists and functionaries who assisted the formation of the Bulgarian army and state institutions. These include Russian officers and generals, such as general Leonid Sobolev, Bulgaria's prime minister in 1882 - 1883, general Alexander Golovin, and functionaries like Sofia's first mayor Piotr Alabin. Almost all of them left Bulgaria after the break-up of relations with Russia in 1886. With the formation of the Principality of Bulgaria in 1878, foreign specialists, entrepreneurs, teachers, workers, and missionaries started arriving in Bulgaria and assisted the building of the new country after five centuries of foreign rule. They were notably from Austria-Hungary and Russia, as well as from Switzerland, Germany, Italy, France, the US and other European nations, who assisted in the modernisation of all aspects of life in the new Bulgarian state. Notable ethnic groups among them were the Czechs and Slovaks, such as Konstantin Josef Jireček, Hermann Škorpil, Karel Škorpil, Jiří Prošek, Ivan Mrkvička, Jaroslav Věšín. Among the temporary or permanent settlers there were also ethnic Jews, Germans and Austrians, Hungarians, Serbs and Montenegrins (settled in a few villages in north-eastern Bulgaria), Croats, Slovenes, Poles, Ukrainians and Rusyns, and others. Czechs, Slovaks, Rusyns and Germans of Protestant and Catholic denomination from Austria-Hungary founded or settled in villages in Northern Bulgaria, such as Voyvodovo, Vratsa Province, Martvitsa (Slovak Mŕtvica, now Podem), Gorna Mitropolia, Brashlyanitsa. The relative freedom of religion allowed Catholic workers and missionaries and Protestant missionaries, mostly from the United States and Great Britain, to establish missions and live for shorter or longer periods in Bulgaria.
A smaller wave of new immigrants arrived to Bulgaria during the socialist regime (1944–1989), where large numbers of foreign students came to study in Bulgarian universities and many of them remained. Most of them married Bulgarian nationals and settled in the country. Also at that time, many Bulgarians married citizens of the then Soviet Union and the Eastern Bloc.
The fall of communism at the end of 1989 saw greater migration to Bulgaria, when large groups of Chinese, Arabs, Russians, Ukrainians, Turks, Vietnamese, Albanians, a number of Armenians from the Republic of Armenia, some Africans, and an increasing number of EU nationals established themselves permanently in Bulgaria. The country's accession to the EU on January 1, 2007, has not yet led to a significant rise in the number of immigrants, although there is a growth in the number of refugees from Afghanistan, Iran, Iraq, Sub-Saharan Africa, Armenia. The slow procedures of granting asylum and refugee status, the low living standard compared to EU average and the postponement of entry to the Schengen area contribute to the low number of refugees and asylum seekers. The recent decade saw a growth of private businesses opened by citizens of Russia, Ukraine, Turkey, China, Bosnia and Herzegovina and the countries in the Middle East, notably Syria and Lebanon. Also during the last decade, Russian, Ukrainian, EU and US citizens purchased holiday properties along the Black sea coast, as well as in the interior.
According to official data, the number of permanent foreign residents in Bulgaria as at 31.12.2008 is 66,806 and the vast majority of these come from Russia (21,309), Ukraine (5,350), the Republic of Macedonia (4,375), Turkey (3,828) and Moldova (2.203). However, this number does not include immigrants who have already obtained Bulgarian citizenship or illegal immigrants. The number of immigrants in Bulgaria is expected to grow as a result of the accession of Bulgaria in the European Union in 2007.
Since the beginning of the Syrian Civil War in 2011, the number of Syrian refugees in Bulgaria grew. Together with the Syrian refugee families, many illegal migrants, mainly males, from countries like Algeria, Morocco, Tunisia, Mali, Niger, Nigeria, Chad, Eritrea, Somalia, Afghanistan, Pakistan, Iran, and Iraq entered illegally Bulgaria through the Bulgarian-Turkish border.