Kashubian Unity Day (, ) is an annual festival celebrated every March 19 to commemorate the first historical written mention of Kashubians, in Pope Gregory IX's Bull of 19 March 1238. In this bull, the Pope referred to Prince Bogislaw I of Pomerania (d. 1187) as duce Cassubie (duke of Kashubia).

Sponsored and coordinated by the Kashubian-Pomeranian Association,