Sandra Den Hamer is to step down as director of the Rotterdam International Film Festival. Den Hamer, who has been involved with the event for more than two decades, will start work as director of Amsterdam's Filmmuseum from September 1.

The Board of the Rotterdam Film Festival will start exploratory talks shortly to appoint a successor.

Den Hamer was made deputy director of the festival in 1991, before co-directing it with Simon Field from 2000. She took over as sole director from March 2004.

She first became involved with Rotterdam when she was appointed by then festival director and founder Hubert Bals to lead CineMart in 1986. The co-production market is now attended by around 900 film professionals each year, who come together to discuss a line-up of 45 film projects.

Den Hamer was also key in developing the Hubert Bals Fund, founded after his death in 1988 to help finance projects from developing countries; more than 60 features have now benefited from the initiative, including Cristian Mungiu's Four Months, Three Weeks And Two Days, selected for competition at this year's Cannes.

Next year's edition of Rotterdam, one of the three largest festivals in the world when judged by public attendance, will run from January 23 until February 3.