Phytophthora ramorum is a recently described species responsible for sudden oak death syndrome and also causes symptoms such as twig wilt and dieback, stem lesions, necrosis of leaf midrib from the petiole and leaf tip necrosis on a range of ornamental plant species. In the USA, a reported epidemic of P. ramorum infections on trees belonging to several families including Fagaceae, Lauraceae and Ericaceae seems to be increasing and there are fears of similar epidemics occurring in woodlands in the UK and mainland Europe. This paper reviews the current state of knowledge and the research efforts being made to understand the biology, manage the disease and prevent widespread outbreaks of P. ramorum infections across Europe and the USA.