The rapid growth in the wireless technology possesses the need of high data rate transmission. This can be accomplished by using Orthogonal Frequency Division Multiplexing (OFDM). It is a particular case of Multi Carrier Modulation (MCM), where high rate data stream is transmitted over low rate subcarriers. The system uses a number of carriers to transmit data simultaneously. The disadvantage of this system is its sensitivity to frequency offset and multipath delay spread as the spectra of OFDM signal is not strictly band limited which causes ICI (Inter Carrier Interference) and ISI (Inter Symbol Interference), resulting in loss of orthogonality between the subcarriers and thereby degrade the system performance. This paper presents various important techniques to estimate the frequency offset in OFDM system.