Geoff Marks began his professional career with the Department of Agriculture in Ceylon, breeding for resistance to rice blast. A postgraduate year in Japan in 1959 led to the award in 1960, of a Rockefeller Foundation scholarship to undertake further postgraduate qualifications at the University of Wisconsin in the U.S.A. After graduation, he migrated to Australia and in July 1963 was appointed Forest Pathologist with the Forests Commission, Victoria. This commenced a long and distinguished career in forest disease research during which he authored or co-authored more than 70 publications and five major books and reviews. Through his own research and the cooperative research he fostered with other organisations in both government and universities, he greatly boosted the study in Australia of eucalypt dieback caused by Phytophthora cinnamomi and eucalypt leaf diseases. He also taught a course in forest pathology at the Victorian School of Forestry, Creswick, and the University of Melbourne. At the time of his premature death from a heart attack he was co-editing another major book, "Diseases and Pathogens of Eucalypts", which was published by CSIRO in 2000 and is a fitting tribute to his outstanding contribution to forest pathology.