In this session, some examples of peculiar protoplanetary disks will be presented, in which it is investigated whether planet formation is possible. For example, indications of planet formation have been found in dwarf disks around very low-mass cool stars, in disks around very massive protostars, as well as in disks around double stars. Although it is not known exactly how planets form in these extreme conditions, it is believed that we are close to finding out.