In any natural ecosystem fungi can be found parasitising many different types of organisms including other fungi, insects, nematodes and plants. In the past these fungi might have been regarded as either a scourge (e.g. the plant pathogens) or just curiosities (e.g. nematode trapping fungi) if they were noticed at all. Today we recognise that these fungi play a significant ecological role in regulating populations of their host organisms across natural environments, and some of them can be utilised as bio-control control agents of major pest species. Interest in fungi as bio-control agents has been fuelled by the recognition that chemical based pest and pathogen control strategies are limited by problems such as toxic residues in the environment and food chain and pest resistance to chemicals. Today there are a number of fungal bio-control agents commercially available in Australia for controlling agricultural pests such as locusts and grasshoppers and plant pathogens such as grey mould in grapes and strawberries and white rot in onions. In addition fungi are being deployed to control invasive weeds such as lantana, water hyacinth and wild blackberry in different Australian states. However the selection and successful development of fungi as new bio-control agents requires an appreciation for and understanding of the ecology of these fungi in both their natural environment and the environments in which they are to be deployed. This presentation will describe the pathway from natural environment to commercial bio-control agent.