The purpose of this chapter is to highlight the strengths and pitfalls of using the Acoustic Emission (AE) technique for damage assessment in masonry structures, such as historical buildings and monuments, that are subjected to high sustained loads or are exposed to seismic risk. Firstly, an overview is presented of AE analysis techniques for damage detection in masonry, with specific reference to the issues that complicate AE sensing in masonry. Secondly, an overview of the authors’ experience with on-site AE monitoring in historical masonry structures is presented and illustrated with several case studies. In particular, the possibility to evaluate damage progress and structural stability from the evolution of AE activity is shown, and, if the position of the defects is not known to begin with, it can be located by making use of a multiplicity of sensors and triangulation techniques. Finally, AE monitoring during experimental campaigns, with AE-based prediction of creep and fatigue failure and a comparison of AE results with other crack measurement techniques during a test on a full-scale masonry wall, is presented.