At the official dinner of a· meeting in May 1939, I was seated next to Max Hansen. When I congratulated him on the well deserved success of his "Aufbau der Zweistoff-Legierungen", he smiled: "yes, it was a struggle with the hydra, and so it has taken me seven years", meaning that whenever he had thought to have finished the phase diagram of a particular system, new evidence would turn up like the new heads of the Greek monster. There is no need to point out the importance of assessed phase diagrams to metallurgists or even anyone concerned with the technology and applica tion of metals and alloys. The information contained therein is fundamental to considerations concerning the chemical, physical and mechanical properties of alloys. Hansen's German monograph was followed by a revised English edition in 1958 with K. Anderko and the supplements by R.P. Elliott (1965) and F.A. Shunk (1969). All those who have made use of these volumes will admit that much diligent labour has gone into this work, necessary to cope with the ever increasing number of publications and the consequent improvements.