Jeanne Demessieux (1921-1968) was one of the leading organists of the twentieth century and an important female composer. The catalog of her compositions contains some of the most difficult pieces in the entire organ repertoire. During the past two decades, there has been a growing interest in Jeanne Demessieux's compositions, mainly through a number of CD releases of her organ music. The purpose of this dissertation is to examine and scrutinize the available information about the life of Jeanne Demessieux. Many inaccuracies concerning her life found in her biographical studies have been corrected in the present work. Furthermore, for the first time ever in a study on Jeanne Demessieux, a complete list of her compositions, including numerous unpublished works and transcriptions, has been included. The organ works which are known today are only one third of Jeanne Demessieux's oeuvre, because the majority of her more than 30 compositions remain unpublished.