On behalf of the Organizing and Scientific Committees, we are pleased to invite you to the IWA Wastewater, Water and Resource Recovery (WWRR) 2021 Conference, which will be held at Poznan University of Technology. This time, the nutrient removal and recovery conference returns to Poland to honour prof. Jan Oleszkiewicz of the University of Manitoba for his long-standing contribution to the development of modern wastewater treatment technologies. The WWRR will provide an excellent space where many distinguished scientists and practitioners from all over the world will share their knowledge and experience. Even though the conference is focused on nutrients, new challenges will also be addressed, including energy efficient technologies, removal of emerging contaminants, resource recovery from sludge and wastewater, and water safety systems. Poznan is the capital of Wielkopolska region in western part of Poland. It is a historical city, cradle of the Polish statehood, and nowadays a modern academic and cultural center. We hope you will join us to present your work, learn from colleagues, make new friends and professional contacts and, of course, enjoy a wonderful spring time in Poland. We are looking forward to meeting you in Poznan.