Abstract Professor Gustaf Olsson has devoted countless hours over many years to Water Science and Technology, Water Supply and Water Practice and Technology as an author, reviewer, editor and Editor in Chief until finally stepping down from all functions in 2021. In order to honour Prof. Olsson's devotion and contribution to the journals, IWA Publishing has compiled a Festschrift: that is, a book made up of contributions from Prof. Olsson's former students, his colleagues (past and present), and of course his friends. As the contributions testify, Gustaf's devotion and influence by far exceeds his work at Water Science and Technology. It has been a joy to read through the testimonies about Gustaf and how he has shaped and influenced lives and academic careers. They express an overwhelming gratitude for the way he has influenced and, in some cases, significantly formed both the professional and personal attitude of those he has touched. It also testifies to great scientific contributions, contributions that are strongly embedded in the water sector industry and with great impact at the time of publishing and clearly also well into the future. His leadership example is a source of inspiration to everybody in the water sector whether in academia or industry. We urge you to read this Festschrift to celebrate Gustaf and get inspired about how to work in service for the greater good of water. ISBN: 9781789063363 (print) ISBN: 9781789063370 (eBook) ISBN: 9781789063387 (ePUB)