The Abruzzo earthquake hit the city of L'Aquila and its surroundings on the April 6, 2009. The aim of this study is to analyze the technical features of unreinforced masonry (URM) buildings and assess their seismic behavior during the Abruzzo 2009 seismic event. The damage induced in the URM constructions of L'Aquila and the suburbs was severe and several such buildings collapsed. This study includes an overview of the dynamic characteristics of the earthquake and the seismic history of the region. The seismic performance of URM buildings is discussed on the basis of both the experience in L'Aquila and the village of Castelvecchio Subequo, during the post-emergency support to the Italian Department of Civil Protection (Dipartimento della Protezione Civile [DPC]), and the field investigation carried out with the patronage of the EU COST Action C26 and the cooperation of the PLINIVS Centre of Naples in three areas of the old city of L'Aquila. The main characteristics of URM buildings, the building behavior and damage are described and reviewed with due respect to the characteristics of the earthquake, as well as with reference to the structural and non-structural characteristics of buildings, using the Italian MEDEA procedure.