By using piezoelectric film the present authors proposed the passive electric potential CT (computed tomography) method and the active pulse echo method for crack identification with the help of the inverse analysis. This paper describes the passive and the active methods using the piezoelectric film and their applications to the identification of cracks. The passive electric potential CT method used the electric potential distribution incurred due to the direct piezoelectric effect on the surface of a piezoelectric film pasted on a cracked body subjected to mechanical load. The present authors proposed a smart layer composed of the piezoelectric film and flexible printed circuit. By applying electric pulse to the smart layer a supersonic wave is emitted due to the inverse piezoelectric effect. The active pulse echo method used the reflected wave observed on the smart layer for the crack identification. The applicability of these methods to the identification of two- and three-dimensional cracks was demonstrated.