Speedy and successful control of a number of insects and weed pests, which had spread into areas other than their original habitats, by biological methods may suggest that “the cream has been skimmed off” in the field of biological control. However, in many instances only comparatively superficial studies have been made and the most obvious and apparently promising natural enemies have been selected as biological control agents. The advent of increasingly frequent and speedy air services to wider and wider areas has opened up more possibilities for the use of the biological control method. Increasing rigidity of quarantine laws and inspection services have not prevented the accidental introduction of exotic insects and weeds into new areas. Increased trade, and particularly facility and speed of air transport, have more than offset the effects of more stringent quarantine measures in this regard. The spread of pest species into new areas will continue and afford additional opportunity for the use of biological control methods. The ecological approach to pest problems is suggested in which an insect pest or its complex of natural enemies should not be considered an isolated entity but in relation to the whole environment, keeping in mind the seasonal changes that occur. Great expansion is indicated in the use of micro-organisms of various types in the control of pests. It is concluded that there is no justification now for considering the method of biological control of decreasing value but that there will be a continued and probably increasing place for this method of control in the future.