Owing to a paucity of documentation, Guillaume Du Fay's biography from 1414 to 1427 is blank; his origins have remained elusive. The earliest reference to him dates from 1409. New documents from Cambrai and a passage in the execution of his will change these circumstances. Du Fay's origins in or near Brussels can now be postulated, and his activity in late 1414 and from late 1417 to 1420 can be documented with precision. In addition, new documentation in Cambrai and Laon confirms and expands biographical implications of works written during this period and adds to the number of works for which a specific occasion can be posited.