thumb|Monastery that was presumably founded by Vaišvilkas (painting by [[Napoleon Orda)]]
Vaišvilkas or Vaišelga (died 18 April 1267) was Grand Duke of Lithuania from 1264 until his death in 1267. He was a son of Mindaugas, the first and only Christian King of Lithuania. This led to the hypothesis that the initial form of the name should have been Vaišvilas. The variant Vaišelga/Vaišalga has gained more popularity in historical writings even though the origins of the element -alg and -elg are not entirely clear.
Biography
Nothing is known about the youth of Vaišvilkas as he entered historical sources only in 1254 when he made a treaty, in the name of his father King Mindaugas, with Daniel of Halych-Volhynia. In the treaty, Halych-Volhynia transfers Black Ruthenia with center in Navahrudak to Lithuania. To solidify the treaty, Daniel's son Shvarn was married to Vaišvilkas' sister. He set off on a pilgrimage to Mount Athos in Greece. However, he did not reach the destination due to wars in the Balkans and returned to Navahrudak.
left|thumb|Work of art, depicting the Grand Duke of Lithuania Vaišvilkas.
In 1264, he escaped an assassination plot by Treniota and Daumantas against his father and two of his brothers. Treniota was murdered by former servants of Mindaugas. Vaišvilkas allied himself with his brother-in-law Shvarn from Halych-Volhynia. They managed to take control over Black Ruthenia and the Duchy of Lithuania. Daumantas, Duke of Nalšia, was forced to flee to Pskov. Suksė (Suxe), another influential duke from Nalšia, fled to Livonia. Vaišvilkas became next the Grand Duke of Lithuania. As a Christian, he tried to maintain friendly relationships with the Teutonic Knights and the Livonian Order. He signed a peace treaty with Livonia regarding trade on the Daugava River.
When in 1267 he decided to go back to monastic life, Vaišvilkas transferred the title of Grand Duke to Shvarn. A year later he was killed by Shvarn's brother, Leo I of Halych, who was angry that Vaišvilkas did not divide the powers between him and his brother.