This study presents the historical impact of Kant's Opus postumum, the philosopher's last unfinished work, in a critical discussion that extends from the time of the work's initial reception in the 19th century up to contemporary Kant research. The common thread that unites this study is a systematic historical reconstruction of the disputes between those interpreters who saw this work as a major departure on the part of the late Kant from the philosophy of his critical writings, and others who saw this posthumously published work as coherently evolving from Kant's earlier transcendental philosophy.