Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers made from ferroelectric piezoceramic wafers attached to safety-critical structure. PWAS transducers enable a large class of structural health monitoring (SHM) applications. The focus of this paper is on the predictive modeling of structurally-attached PWAS. After a brief introduction, the paper reviews the PWAS-based SHM principles. Then, it follows with a discussion of shear-lag analysis, the transfer matrix method approach and the investigation of power and energy transduction between PWAS and structure. Finally, the paper presents a multi-physics finite element (MP-FEM) simulation. The paper ends with summary and conclusion.