The objective of this paper is to present models for the design of confined masonry structures based on the available experimental data. In particular, this study deals with in-plane response of masonry walls subjected to lateral forces, with emphasis on aspects of initial stiffness, strength and deformation capacity. The experimental information used in this work comprises tests performed at the Structures Laboratory of the Catholic University of Peru. Results indicate that stiffness can be calculated considering a wall cross-section inertia using the transformed cross-section concept with the appropriate Young's moduli for concrete and masonry.