Measurement of deformation or shape differences of two objects is impossible in usual holographic interferometry. Difference holographic interferometry (DHI) overcomes the difficulties by producing a comparing technique for measurement of displacement fields and shapes of different objects and by being powerful in the case of large deformations. The main feature of DHI is that holographically recorded waves are used for illumination by wavefront reversal. It works without the need to consider different microstructures of object surfaces. A few realizations of the technique are presented.