Book excerpt: This book is dedicated to the memory of Ole-Johan Dahl who passed away in June 2002 at the age of 70, shortly after he had received, together with his colleague Kristen Nygaard, the ACM Alan M. Turing Award: "For ideas fundamental to the emergence of object-oriented programming, through their design of the programming languages Simula I and Simula 67." This Festschrift opens with a short biography and a bibliography recollecting Ole-Johan Dahl's life and work, as well as a paper he wrote entitled: "The Birth of Object-Orientation: the Simula Languages." The main part of the book consists of 14 scientific articles written by leading scientists who worked with Ole-Johan Dahl as students or colleagues. In accordance with the scope of Ole-Johan Dahl's work and the book's title, the articles are centered around object-orientation and formal methods.