This paper focuses on any straight bar, herein called “anchor”, inserted within a hole drilled into a masonry structure, installed orthogonally to the masonry surface, and bonded to the masonry either with an anchoring material or without (adhesive or mechanical anchors). The anchor is subjected to a transverse force applied at the end that protrudes from the masonry (i.e., a shear force having direction parallel to the masonry surface), while no appreciable axial force is applied to the anchor (shear anchor). In brief, the paper is devoted to the postinstalled horizontal anchor that transfers vertical loads from a horizontal structure to a vertical masonry structure. On site experiments on real anchors allowed the author to establish the mechanical assumptions that govern the behavior of the shear anchor. Based on those assumptions, an analytical (closed form) model was created. The model is comprised of a function that gives the ultimate contact pressures, and a two-equation system whose solution is the maximum shear force that the anchor can bear, therefore called “shear strength”. The model also provides the elastic limit shear strength. The data to be entered into the model is composed of the geometry of the anchor and the strength of the masonry. The paper presents the experimental campaigns, the model, the application of the model to case studies, and a comprehensive discussion. The results put forward the optimal technical solutions for the masonry shear anchor, which are described.