Lev Krevza's "Defense of Church Unity" (1617), on the Uniate side, and Zaxarija Kopystens'kyj's "Palinodia" (1621), a monumental defense of the Eastern Church, are arguably the most erudite, comprehensive, and persuasive works on the ecclesiastical debate between these two groups. This two-volume work illuminates the intense struggle ignited when, at the time of the Union of Brest (1596), a large part of the Ruthenian ecclesiastical hierarchy declared itself in communion with the Roman Catholic Church. Bohdan Struminski provides English translations from the original Ruthenian and Middle Polish texts.