Arthrobotrys oligospora, a predacious fungus of nematodes, has been very useful in understanding the relationship between nematophagous fungi and their nematode hosts. Arthrobotrys oligospora is by far the most common nematode-trapping fungus with the characteristic ability of forming adhesive trapping nets once in contact with nematodes. This review highlights the versatility and development of A. oligospora as a system to identify and characterize the ecology and biology of nematode-trapping fungi. Using A. oligospora, advances in our knowledge of nematophagous fungi have been made through the discovery of special traits and virulence determinants involved in the pathogenic process, or by creating new ways of presenting these factors to the target nematodes. We argue for an increased role for A. oligospora in complementing other model systems in biological control research.