In September 2016, Jørgen S. Nielsen celebrated his 70th birthday. The articles in the present volume are collected in expectation of that joyous occasion. As often is in academia, it is only now that we have been able to gather and publish all the contributions from friends and colleagues. As will be evident in the following, this year also marks a number of jubilees in Jørgen S. Nielsen’s life and career. In this introductory article, we give an overview of his biography, a selection of the themes in his work, and return to look at the impact and timeliness of his contribution to the study of Islam and Muslims. Looking through his biography here, readers might want to cross-reference with the highlighted bibliography printed at the back of the volume, to see how his production corresponds with the stages and positions of his career. These articles collected in this volume are introduced and we see how they indeed echo the themes and curiosity in Jørgen S. Nielsen’s own exploration of the multitude of Muslims in Europe.