Suvalkija or Sudovia (Lithuanian: Suvalkija or Sūduva) is the smallest of the five cultural regions of Lithuania. Its unofficial capital is Marijampolė. People from Suvalkija (Suvalkijans) are called suvalkiečiai (plural) or suvalkietis (singular) in Lithuanian. It is located south of the Neman River, in the former territory of Vilkaviškis bishopric. Historically, it is the newest ethnographic region, as its most distinct characteristics and separate regional identity formed during the 19th century when the territory was part of Congress Poland. It was never a separate political entity, and even today, it has no official status in the administrative division of Lithuania. However, it continues to be the subject of studies focusing on Lithuanian folk culture of the 19th and early 20th centuries.

Most of Lithuania's cultural differences blended or disappeared during the Soviet occupation (1944–1990), remaining the longest in southeastern Lithuania. The concept remains popular among Lithuanian people. A 2008 survey of freshmen and sophomores (first- and second-year students) at Kaunas' Vytautas Magnus University found that 80% of the students continued to identify themselves with one of the regions. Efforts are made to preserve, record, and promote any remaining aspects of the original folk culture.

Suvalkija is in the southwest part of Lithuania. The largest city located entirely within the region in Marijampolė, which is considered to be the capital, though not in a strict political sense. Lithuania's second-largest city of Kaunas is bisected by the Neman River, placing the southern part of the city in this region and the northern part in Aukštaitija.

The largest cities (by population, not including the portion of Kaunas within this region) are:

In Lithuania, three different names have been applied to the region, causing some confusion:

In recent years, there has been public debate as to which name, Suvalkija or Sudovia, is preferable. Historians have argued that Sudovia is an anachronism that refers to the land in the 13th and 14th centuries. One commentator labeled the effort to rename the region as "neotribalism" – an artificial attempt to find connections with the long-extinct tribe. Supporters of Sudovia protested against using a term imposed on the region by the Russian Empire, especially since the city of Suwałki is in Poland, and the current region has no connection with it. They have also argued that the term Suvalkija is a fairly recent and artificial political development, popularized by Soviet historians, and that the more archaic Sudovia more correctly reflects the region's historical roots. The suffix -ija is not generally used in the Lithuanian language to derive placenames from city names (the only exception is Vilnija, used to describe the Vilnius Region). An official petition from the Council for Protection of the Suvalkija Regional Ethnic Culture to the Commission of the Lithuanian Language, requesting an official name change from Suvalkija to Sudovia, was rejected in 2005. The Commission based the decision on its finding that Suvalkija prevails in both academic literature and everyday life.

Suvalkija is roughly subdivided into two areas, inhabited by Zanavykai (singular: Zanavykas) and by Kapsai (singular: Kapsas). Zanavykai occupy northern Suvalkija, in the area approximately bounded by the Neman, Šešupė, and Višakis Rivers. Before 1795, that part of Suvalkija lay within the Eldership of Samogitia, while the rest was within the Trakai Voivodeship. Šakiai is considered to be the capital of this subregion, sometimes called Zanavykija. Another important center is in Veliuona. The name Zanavykai is derived from the Nova River, a tributary of the Šešupė River. People who lived beyond the river (Polish: za Nawą) became known as Zanavykai. The prefix za- and the suffix -yk are Slavic. To correct this, linguists proposed naming the group Užnoviečiai or Užnoviškiai, terms which also mean "beyond the Nova river" but follow Lithuanian language precedents. However, this proposal did not gain popular support and the term Zanavykai is still widely used.

Kapsai inhabits southern Suvalkija, with major centers in Marijampolė and Vilkaviškis. The term is not used by local inhabitants to identify themselves, but is rather a term coined by linguists; it did not gain much popularity in the public. When linguists classified Lithuanian language dialects, they identified two major sub-dialects in Suvalkija: one in the territory inhabited by Zanavykai and another in the south. Southerners pronounced the word kaip (how) as kap. This distinct characteristic earned them the name Kapsai, but they could also be called Tepsai as they pronounced word taip (yes) as tep. A revised classification of the dialects, proposed in 1965 by linguists Zigmas Zinkevičius and Aleksas Girdenis, eliminates this distinction and deems the local dialect a sub-dialect of Western Aukštaitian dialect. However, other cultural distinctions between Zanavykai and Kapsai exist, including their traditional clothing styles.