In HEP, the momentum or energy of primary particles are reconstructed using the amount of charge or energy deposited in the detector by their secondaries. The calibrations for the same are done with the help of simulated data. However, the resolution of detectors, statistical fluctuations, contribution of background and other factors introduce bias in the momentum or energy reconstruction. This talk will describe the correction of this bias using the method of unfolding with special focus on the Bayesian iterative unfolding method. The method of unfolding finds a wide range of applications in HEP, spanning over colliders as well as astroparticle experiments.