Masonry construction comprises a large protion of building construction in the U.S. and the world. Reinforced masonry construction use is increasing in moderate to higher seismic zones because of its apparent features of economy, fire safety, architectural flexibility, and ease of construction. The present state of masonry structural analysis and design and materials and construction technologies do not enable and accurate prediction of building behavior under lateral loads such as seismic loads. This research project will determine the in-plane behavior of masonry wall structures subjected to earthquake motions. Parameters that will be examined in the experimental research project include wall type and configurations, size and location of openings, masonry type, grouting procedures, and reinforcement amount and distribution. The results of the research will be used to establish rational limit state design metholologies for reinforced masonry.