Polonization or Polonisation (Polish: polonizacja; Belarusian: паланізацыя, romanized: pałanizacyja; Ukrainian: полонізація, romanized: polonizatsiya; Lithuanian: polonizacija; Samogitian: puoluonėzacėjė) is the acquisition or imposition of elements of Polish culture, in particular the Polish language. This happened in some historic periods among non-Polish populations in territories controlled by or substantially under the influence of Poland.
Like other examples of cultural assimilation, Polonization could be either voluntary or forced. It was most visible in territories where the Polish language or culture was dominant or where their adoption could result in increased prestige or social status, as was the case with the nobilities of Ruthenia and Lithuania. To a certain extent, political authorities have administratively promoted Polonization, particularly during the interwar period and in the period following World War II.