The Treaty of Trentschin was an agreement signed between King Casimir III of Poland and King John of Bohemia by the agency of Casimir's brother-in-law King Charles I of Hungary on 24 August 1335 at Trencsén Castle in the Kingdom of Hungary (present-day Trencín, Slovakia). The treaty initiated the transfer of the suzerainty over the former Polish province of Silesia to the Kingdom of Bohemia.