The chalcidoid wasps of the genus Monacon develop as parasites of the larvae of ambrosia beetles (mainly Platypodidae) in the tropical forests of the Old World. Their known hosts are reviewed. A key is given to species, which are treated in two groups, according to geographical region: first the Indo-Australian species, then the African ones. The previously known Indo-Australian species come from India and Bangladesh (two), North Borneo (one) and the Philippines (one), and another 14 are here described as new: two from Sri Lanka, two from Burma, two from West Malaysia, one from both West Malaysia and the Philippines, two from the Philippines only, four from Papua New Guinea only and one from both Papua New Guinea and the Philippines. Three African species were previously known from Zaire; one of them has now been found also in Uganda. Three species are described as new: one from Uganda, one from both Uganda and Nigeria and one from Kenya.