Polish was once a lingua franca in various regions of Central and Eastern Europe, mostly due to the political, cultural, scientific and military influence of the Polish-Lithuanian Commonwealth. Although no longer having as great an influence outside of Poland, due in part to the dominance of the Russian language, it is still sometimes spoken or at least understood in western border areas of Ukraine, Belarus and Lithuania as a second language. It shares some vocabulary with the languages of the neighboring Slavic nations, most notably with Czech, Slovak, Ukrainian and Belarusian.
The Polish language is the most widely-spoken of the Slavic language subgroup of the Lechitic languages which include Kashubian (the only surviving dialect of the Pomeranian language) and the extinct Polabian language. The three languages, along with Upper and Lower Sorbian, Czech and Slovak, belong to the West branch of Slavic languages.
Polish is mainly spoken in Poland. In fact, Poland is one of the most homogenous European countries in terms of its mother tongue, as close to 97% of Polish citizens declare Polish as their mother tongue. After the Second World War the previously Polish territories annexed by the USSR retained a large amount of the Polish population that was unwilling or unable to migrate toward the post-1945 Poland and even today ethnic Poles in Lithuania, Belarus, and Ukraine constitute large minorities. In Lithuania 9 percent of the population declared Polish to be their mother tongue. It is by far the most widely used minority language in the Vilniaus Apskritis (Vilnius region) (26% of the population, according to the 2001 census results), but it is also present in other apskritis. In Ukraine, Polish is most often used in the Lwów and Luck regions. Western Belarus has an important Polish minority, especially in the Brzesc and Grodno regions.
There are also significant numbers of Polish speakers in Argentina, Australia, Austria, Azerbaijan, Brazil, Canada, Czech Republic, Estonia, Finland, Germany, Greece, Hungary, Israel, Ireland, Kazakhstan, Latvia, New Zealand, Romania, Russia, Slovakia, UAE, the UK and the United States.