Rusyns, also known as Carpatho-Rusyns, Carpatho-Russians, Ruthenians, or Rusnaks, are an East Slavic ethnic group from the Eastern Carpathians in Central Europe. They speak Rusyn, an East Slavic language variety, treated variously as either a distinct language or a dialect of the Ukrainian language. As traditional adherents of Eastern Christianity, the majority of Rusyns are Eastern Catholics, though a minority of Rusyns practice Eastern Orthodoxy.

Rusyns primarily self-identify as a distinct ethnic group and are recognized as such in all countries where they exist, with the exception of Ukraine, which officially classifies Rusyns as a sub-group of Ukrainians. In Croatia, Hungary, Poland, Romania, Serbia, and Slovakia, Rusyns have official minority status. Some Rusyns identify more closely with their country of residence (i.e. Polish, Slovak), while others self-identify as a branch of the Ukrainian people.^{[page needed]}

Rusyns are descended from an East Slavic population that inhabited the northeastern regions of the Eastern Carpathians. In those regions, there are several Rusyn groups, including Dolinyans, Boykos, Hutsuls and Lemkos. Since the Revolutions of 1989 toward the end of the 20th century, there has been a revival in Rusyn culture and identity. Of the estimated 1.7 million people of Rusyn origin, only around 110,000 have been officially identified as such in recent (c. 2012) national censuses.

The term Rusyn (Rusyn: Русин, plural Русины, Rusynŷ) originates from the archaic ethnonym "Rus'". The respective endonymic adjective has traditionally been rusʹkŷi (руськый m., руська f., руське/руськое n.), though rusynʹskŷi (русиньскый, русинськый, русинский, русиньскій, русински) has also been used; even more so after 1989. In interwar Czechoslovakia, Ruthenia was called Rusinsko in Czech; sometimes rendered Rusinia or Rusynia in American-Rusyn publications.

Carpatho-Rusyn or Carpatho-Ruthenian (Karpato-Rusyny) is the main regional designation for Rusyns, especially in North America. The term refers to Carpathian Ruthenia (Karpatsʹka Rusʹ), which is a historical cross-border region encompassing Subcarpathian Rus' (in northeastern Slovakia and Ukraine's Zakarpattia Oblast), Prešov Region (in eastern Slovakia), the Lemko Region (in southeastern Poland), and Maramureş (in north-central Romania). In the Lemko region, the endonym Lemko (pl. Lemkŷ) became more common in the twentieth century, along with Lemko-Rusyn since the 1990s.

The variant Rusnak (Руснак; plural: Rusnakŷ or Pannonian-Rusyn, Rusnatsi) was also (and still is) used as an endonym; particularly by Rusyns outside the Carpathians in Vojvodina, Serbia and Slavonia, Croatia. However, they may also referred to as Vojvodinian Rusyns (voivodianski Rusnatsi), Bachka-Srem Rusyns (bachvansʹko-srimski rusnatsi), or formerly as Yugoslav Rusyns (iuzhnoslaviansʹki Rusnatsi).

Other terms such as Ruthene, Rusniak, Lemak, Lyshak, and Lemko are considered by some scholars to be historic, local, or synonymic names for these inhabitants of Transcarpathia. Others hold that the terms Lemko and Rusnak are simply regional variations for Rusyns or Ruthenes. Rusyns have at times also been referred to as Uhro-Rusyn (Uhro-Rus) in the regions of Prešov, Slovakia and Carpathian Ruthenia.

From the mid 1800s and well into the mid 1900s, many Catholic and Orthodox Rusyns in Europe and the United States referred to themselves as Carpatho-Russians or sometimes as Carpathian Russians. This terminology was also popular with some foreign authors and was and is still being used within the Rusyn diaspora.^{[citation needed]}