The book presents the history of ICMI trough a prosopographical approach. In other words, it pays a lot of attention to the actors of the International movement. The portraits of the members of the ICMI Central Committees (1908-1936) and ICMI Executive Committees (1952-2008), and other eminent figures in ICMI history, who have passed away in the first 100 years of its life, are the guiding thread of the volume. Each portrait includes: * Biographical information * An outline of the various contributions made by the individual in question to the study of problems pertaining to mathematics teaching/education * Primary bibliography * Secondary with particular attention to the publications concerning the teaching of mathematics * Images: photos, book frontispieces, relevant manuscripts The authors of the portraits (30 altogether) are researchers in the history of mathematics, mathematics, and mathematics education. The focus on the officer's role within ICMI and on his/her contributions to mathematics education, make the portraits different from usual biographies. In particular, since most officers were active mathematicians, the portraits shed light on aspects of their lesser-known activity. Connecting chapters place the action of these figures in the historical context and in the different phases of ICMI history.