Ash trees have considerable economic, cultural and environmental value on the island of Ireland. However, European ash (Fraxinus excelsior L.) is currently under threat from the invasive ascomycete pathogen Hymenoscyphus fraxineus. This pathogen is the causal agent of ash dieback disease, which was initially reported in Poland in 1992. Hymenoscyphus fraxineus has since spread across Europe and the first recorded case of the disease on the island of Ireland was in 2012 at a forestry plantation in Co. Leitrim. The pathogen is now present in all 26 counties in Ireland and 6 counties in Northern Ireland, and it is considered unfeasible to eradicate. The spread of ash dieback disease is reflected in recent policy changes, which focus on management rather than eradication strategies. Since the first formal description of H. fraxineus in 2006, considerable research efforts have been made by the international scientific community to understand the biology of the pathogen and to develop management strategies against it. This review provides an update of current knowledge of H. fraxineus biology and infection. We then explore examples of mitigation techniques that have been trialled in Europe, in order to identify strategies that are feasible for disease management at a local level on the island of Ireland. Finally, we outline five key avenues of research that have the potential to provide breakthroughs in methods to protect valuable F. excelsior resources.