The unpublished writings of Helmut Hasse, consisting of letters, manuscripts and other papers, are kept at the Handschriftenabteilung of the University Library at Göttingen. Hasse had an extensive correspondence; he liked to exchange mathematical ideas, results and methods freely with his colleagues. There are more than 8000 documents preserved. Although not all of them are of equal mathematical interest, searching through this treasure can help us to assess the development of Number Theory through the 1920s and 1930s.

The present volume is largely based on the letters and other documents its author has found concerning the Brauer-Hasse-Noether Theorem in the theory of algebras; this covers the years around 1931. In addition to the documents from the literary estates of Hasse and Brauer in Göttingen, the author also makes use of some letters from Emmy Noether to Richard Brauer that are preserved at the Bryn Mawr College Library (Pennsylvania, USA).

Autorentext
The author is Professsor emeritus at the University of Heidelberg, Germany. He is a member of the Heidelberger Academy of Sciences and  of the Academy Leopoldina at Halle. He has been awarded an honorary doctors degree from the University of Essen.

Zusammenfassung
The legacy of Helmut Hasse, consisting of letters, manuscripts and other - pers, is kept at theHandschriftenabteilung of the University Library at Gottin- ¨ gen.Hassehadanextensivecorrespondence;helikedtoexchangemathematical ideas, results and methods freely with his colleagues. There are more than 8000 documents preserved. Although not all of them are of equal mathematical - terest, searching through this treasure can help us to assess the development of Number Theory through the 1920s and 1930s. Unfortunately, most of the correspondence is preserved on one side only, i.e., the letterssenttoHasse are availablewhereasmanyoftheletterswhichhadbeensentfromhim,oftenha- written, seem to be lost. So we have to interpolate, as far as possible, from the repliestoHasseandfromothercontexts,inorderto?ndoutwhathehadwritten 1 in his outgoing letters. The present article is largely based on the letters and other documents which I have found concerning the Brauer-Hasse-NoetherTheorem in the theory of algebras; this covers the years around 1931. Besides the do- ments from the Hasse and the Brauer legacy in Gottingen, ¨ I shall also use some letters from Emmy Noether to Richard Brauer which are preserved at the Bryn Mawr College Library (Pennsylvania, USA).

Inhalt
The Main Theorem: Cyclic Algebras.- The Paper: Dedication to Hensel.- The Local-Global Principle.- From the Local-Global Principle to the Main Theorem.- The Brauer Group and Class Field Theory.- The Team: Noether, Brauer and Hasse.- The American Connection: Albert.- Epilogue: Käte Hey.