Emma Letitia Johnston AO FAA FTSE FRSN (born 1973) is the Dean of Science at the University of New South Wales and President of Science & Technology Australia. She is an authority in marine ecology and a former Pro Vice-Chancellor (Research) at UNSW. Johnston is head of the Applied Marine and Estuarine Ecology Lab at UNSW and has led major projects for industry, government, the Australian Research Council and the Australian Antarctic Science Program. Johnston was the inaugural Director of the Sydney Harbour Research Program at the Sydney Institute of Marine Science.