The Christianization of Lithuania (Lithuanian: Lietuvos krikštas) occurred in 1387, initiated by King of Poland and Grand Duke of Lithuania Władysław II Jagiełło and his cousin Vytautas. It signified the official adoption of Christianity by Lithuanians, the last pagan nation in Europe. This event ended one of the most complicated and lengthiest processes of Christianization in European history.
Lithuanians' contacts with the Christian religion predated the establishment of the Duchy of Lithuania in the 12th century. The first known record of the name Lithuania (Litua), recorded in the Annals of Quedlinburg in 1009, relates to Chalcedonian missionaries led by Bruno of Querfurt, who baptised several rulers of the Yotvingians, a nearby Baltic tribe. However, Lithuanians had more active contacts with the Kievan Rus' and subsequent Eastern Slavic states, which had adopted Eastern Orthodox Christianity following the Christianization of Kievan Rus' in the 10th century.
As the dukes of Lithuania extended their dominion eastwards, the influence of the Slavic states on their culture increased. Their subordinates and the people followed their example, borrowing, for instance, many of the East Slavic versions of Christian names in the 11th - 12th centuries. This borrowing became increasingly widespread among the pagan population in Aukštaitija, though much less so in Samogitia. The influence of Orthodox Christianity on pagan Lithuanian culture is evidenced in about one-third of present-day Lithuanian surnames which are constructed from baptismal names are Old Church Slavonic in origin. In addition, the Lithuanian words for "church", "baptism" and "fast" are classed as 'loanwords from Russian rather than Polish.'