This rapid PRA shows: Xylella fastidiosa is a plant-pathogenic bacterium which infects a very wide range of plants. It is already heavily regulated to reduce the likelihood of it entering the UK. In some host species, impacts can be severe and the plant or tree can be killed rapidly. Other hosts have latent infections, or may remain asymptomatic (but still be capable of spreading the disease) for several years before succumbing to the bacterium. Xylella fastidiosa is native to the Americas, but has been spread to countries elsewhere in the world, including parts of Europe. There are several subspecies of X. fastidiosa, which have different host ranges. Xylella fastidiosa is vectored by a number of xylem-feeding hemipteran insect species, including some which are widespread in the UK. At least parts of the UK are likely to prove suitable for X. fastidiosa to establish, but it is unclear what levels of damage it may be able to cause to plants in the UK. If an outbreak were to occur in the UK, the greatest impacts are expected to be social (though the assessment of potential social impacts is made with medium confidence, while confidence in potential economic and environmental impacts is low, indicating the uncertainty about the magnitude of direct impacts which might occur in the UK). Leaf scorches and other symptoms could be visible on amenity trees causing public concern, impacts on horticultural businesses could be severe, and this is already a 2 high-profile pest in the media. Other impacts could occur due to the response required to keep the UK free of X. fastidiosa, reputational damage to the UK, and potential restrictions on exports if eradication were to be unsuccessful. However, substantial uncertainties remain about many key aspects of X. fastidiosa, and it has not proved possible to quantify the risk to the UK with any degree of confidence.