For more than 35 years, Ulrich Frank has shaped Wirtschaftsinformatik as a scientific discipline through thoughtful and sophisticated research contributions and his numerous contributions to the scientific community.Informing Possible Future Worlds is the Festschrift in honour of Ulrich Frank on the occasion of his 65 th birthday. The Festschrift includes twenty-three essays written by friends, colleagues, and fellow researchers in recognition of Ulrich's contributions to Wirtschaftsinformatik research and the scientific community. Each essay is a personal and unique 'birthday present' to Ulrich Frank written exclusively for the Festschrift. From original research contributions to more personal reflections, the essays cover a wide range of topics, themes, and fields -just like Ulrich Frank's contributions.For more than 35 years, Ulrich Frank has shaped and promoted Wirtschaftsinformatik as a scientific discipline through his thoughtful and sophisticated research contributions and his numerous contributions to the scientific community. He has initiated, engaged in and promoted scientific discourse nationally and internationally, inspired, encouraged and guided young researchers, and played an outstanding part in the Wirtschaftsinformatik community.Starting with his Diplomarbeit in 1982 on 'Die Problematisierung von Zielbildungsprozessen in Unternehmungen durch die Betriebswirtschaftslehre unter besonderer Berücksichtigung des Verhältnisses von Wissenschaft und Praxis' (supervised by Erwin Grochla at the Universität zu Köln), Ulrich has cultivated his interest not only in Betriebswirtschaftslehre and Wirtschaftsinformatik, Software Engineering and Conceptual Modelling, but also in the Philosophy of Science, the Philosophy of Language, the Sociology of Knowledge and in Organisational Sociology. For his Diplomarbeit, he read Albert, Feyerabend, Mittelstrass, and Popper, among others, and reflected on organisational goal-setting ('Zielbildungsprozesse') from multiple, complementary perspectives -a lifelong leitmotiv he later incorporated in his Multi-Perspective Enterprise Modelling (MEMO) method.An avid reader and bibliophile, Ulrich must have learned about Niklas Luhmann, the German sociologist working at Universität Bielefeld, Ulrich's hometown, likely in his teens, and started his own personal discourse with Luhmann's writings, and from there on expanded his readings. At about the same time, Ulrich started to program computers, developed and sold his first software application, and, most importantly, discovered Smalltalk, the programming language created by Alan Kay and others at Xerox PARC's Learning Research Group -which has strongly influenced him to this day and which he has admired ever since.Following his discovery of Smalltalk, he took a deep dive into Object-Oriented Programming and Object-Oriented Modelling that took him to take a minor in Angewandte Informatik (Applied Informatics) at the Universität zu Köln during his graduate studies.vii His doctoral research with Alfred Kieser at Universität Mannheim ...