The impedance based structural health monitoring (SHM) techniques have utilized the electro-mechanical coupling property of piezoelectric materials (piezo-impedance transducers), due to their self-sensing nature (ability to act both as actuators and sensors), and its diminutive in shape and size, cost effectiveness and ease of installation. The adhesive bond acts as an elastic medium which facilitates the transfer of stresses and strains developed due to piezo displacement and also couples the impedance of PZT patch with that of the host structure. The sensitivity of the electro-mechanical impedance (EMI) technique can be enhanced by understanding shear mechanism phenomena of the adhesive layer. This paper reviews the existing shear lag models and discuss the recent advances in impedance based coupled piezo-structural model duly considering the shear lag effect with all responsible piezo-mechanical parameters. © 2015 SPIE.