The author's PhD addressed the sustainable management of mixed dipterocarp forests. The study included fieldwork at the Wanariset station and the nearby Wanariset Research Forest in East Kalimantan, Indonesia. Part of the research was carried out in greenhouses of the Wageningen Agricultural University in the Netherlands. The author worked on this research in East-Kalimantan since 1985, first in a cooperation project between Indonesia and the Netherlands called 'Mycorrhiza in the tropical rain forest (Dipterocarpaceae)' and since late 1987 within the framework of the Tropenbos-Kalimantan project. Dipterocarpaceae are mainly confined to Southeast Asia and many species within this family are commercially important timber producers like â€œlaganâ€ and â€œmarantaâ€. A major problem in the management of these species has been the production of good planting stock. The study also investigated the role of ectomycorrhiza in the regeneration of Dipterocarp forests in detail. Some important elements of this study included the inventory of ectomycorrhizal mushrooms, their relationship to specific Dipterocarp species and the influence of physical factors on Dipterocarp ectomycorrhiza. The outcome of this study resulted in several practical applications in the propagation of Dipterocarp species, now enabling the successful replanting of Dipterocarp species.