The present work is aimed at conducting studies of vulnerability and seismic risk of building structures. The objective of such studies is to try to predict the damage expected in a structure, in a group of structures or in an entire urban area, for an earthquake of certain characteristics. Once the expected damage is known, solutions can be found to reduce the losses that future earthquakes would cause. The wide use that reinforced concrete has had as building material in recent decades requires an in-depth study of the seismic behavior and of the degree of vulnerability of buildings constructed with this material. For this reason, in this monograph a methodology for assessing the vulnerability and seismic risk of said buildings is applied. One of the central aspects studied is related to the use of the probabilistic simulation of the seismic behavior of the structures. The method of the vulnerability index applied to reinforced concrete structures is described, which is used for the large-scale evaluation of the seismic quality of the structures. Then the methodology is applied to the study of the seismic vulnerability of the structures, obtaining as a result vulnerability functions and damage probability matrices. Using these curves, the probabilistic seismic risk study is carried out in the central area of Barcelona, Spain, calculating the annual probable loss rates in the area and analyzing the possible costs of insurance against earthquakes. Some seismic damage scenarios obtained with the help of a geographic information system are also developed. Finally, the results and measures to reduce the risk in the area are analyzed.