Technical Abstract: Eutypa dieback of Vitis (grape) is caused by the Ascomycete fungus Eutypa lata. The pathogen infects grapevine through wounds, and cause wood canker and dieback symptoms. E. lata has been identified in all major grape production areas in the world. The first report of Eutypa dieback from northeastern United States identifies the causal agent as E. lata. However, our recent studies questioned the species identity of the causal agent of Eutypa dieback in these regions. Our objectives were to: 1) survey Eutypa-affected vineyards in northeastern US (CT, MA, MI, NY, OH, RI) and Ontario, Canada and evaluate disease incidence; 2) identify the Eutypa species using multi-gene phylogeny, microsatellite analysis and secondary metabolite profile; 3) determine the pathogenicity of the Eutypa species recovered. Incidence of Eutypa dieback increased with the density of vines. Based on phylogenetic analyses of three nuclear loci (rDNA ITS, beta-tubulin), we identified E. lata, E. laevata, and two new undescribed species that are closely related to E. lata. E. lata was only found in two vineyards (Rhode Island and Ontario) suggesting that these collections may represent introductions from outside the eastern U.S and Canada. All Eutypa species produced phytotoxins and were pathogenic on V. labruscana ‘Concord’ and V. vinifera ‘Chardonnay’.