In early 1947, American officials in Germany stumbled across a document. Headed "Secret Reich matter," it summarized the results of a meeting of top Nazi officials that took place on January 20, 1942, in a grand villa on the shore of Berlin's Lake Wannsee.<BR>On one level, this document offered clarity: known as the Wannsee Protocol (and included here in full), it tallied up the Jews in Europe, carefully classified half and quarter Jews, and above all laid the groundwork for a "final solution to the Jewish Question." Yet the Protocol, among the most shameful documents in history, remains deeply puzzling. How can we understand this businesslike discussion of genocide? And why was the meeting necessary? Hundreds of thousands of Jews had already been shot by squads in Russia or gassed in the camp at Chelmno. Test murders had been carried out in Auschwitz. Indeed, the most remarkable thing about the Wannsee Conference is that we do not know why it took place.