September 1939 has hardly been given attention by Belgian scholars. The German attack on Poland and the start of the Second World War obviously occurs in general history surveys of WW II, but no original research on sources has been published on the Belgian reaction to the events in Poland. This can hardly been explained by a lack of attention to Belgian-Polish relations, which actually appears to be extremely well developed within Belgian historiography. It is rather caused by the character of the historiography on Belgium and the Second World War. This has been determined by the way Belgian society has experienced the war years and its immediate consequences, and this explains the absence of debate about September 1939. All in all, in Belgian national history and memory, not September 1939 but May 1940 forms the caesura marking the end of the interwar period and beginning of, or at least the Belgian entrance in, the Second World War.