After the Union of Lublin in 1569 and the formation of the Polish–Lithuanian Commonwealth Ukraine fell under the Polish administration, becoming part of the Crown of the Kingdom of Poland. The period immediately following the creation of the Commonwealth saw a huge revitalisation in colonisation efforts. Many new cities and villages were founded & links between different Ukrainian regions, such as Galicia and Volyn were greatly extended.

New schools spread the ideas of the Renaissance; Polish peasants arrived in great numbers and quickly became mixed with the local population; during this time, most Ukrainian nobles became polonised and converted to Catholicism, and while most Ruthenian-speaking peasants remained within the Eastern Orthodox Church, social tension rose. Some of the polonized mobility would heavily shape Polish culture, for eample, Stanisław Orzechowski.

Ruthenian peasants who fled efforts to force them into serfdom came to be known as Cossacks and earned a reputation for their fierce martial spirit. Some Cossacks were enlisted by the Commonwealth as soldiers to protect the southeastern borders of Commonwealth from Tatars or took part in campaigns abroad (like Petro Konashevych-Sahaidachny in the battle of Khotyn 1621). Cossack units were also active in wars between the Polish–Lithuanian Commonwealth and Tsardom of Russia. Despite the Cossack's military usefulness, the Commonwealth, dominated by its nobility, refused to grant them any significant autonomy, instead attempting to turn most of the Cossack population into serfs. This led to an increasing number of Cossack rebellions aimed at the Commonwealth.