We would like to invite you to participate in the “9th MITOCHONDRION 2021 on-line” Conference. It will take place on ZOOM WEBINAR platform. The Conference is the continuation of bioenergetics meetings organized in Poland in recent years: in Warsaw, Poznań, Wrocław, and Mikołajki. The meeting is organized by the Nencki Institute of the Polish Academy of Sciences, the Polish Biochemical Society (Bioenergetics Section), and the Polish Biophysical Society. The Program of the Conference will include the Key Note Lecture and short presentations by PhD Students. The topics of the Conference will cover metabolism regulation, cellular and molecular bioenergetics and biophysics of membranes. The main organizers of the Conference “9th MITOCHONDRION 2021 on-line” are Adam Szewczyk (co-chair; Bioenergetic Section of Polish Biochemical Society), Piotr Bednarczyk (co-chair, President of Polish Biophysical Society), Piotr Koprowski, Bogusz Kulawiak, Antoni Wrzosek and Monika Żochowska from the Nencki Institute PAS.