Abstract: In recent years, ultra-cold atoms opened an exciting new direction of condensed matter physics. Radio frequency spectroscopy provides an important tool to understand energy gap and quasi-particle dispersion in ultra-cold Fermi gases. Here we present a systematic study of the RF spectra of Fermi gases in the BCS-BEC crossover. We discuss the effects of traps, population imbalance, final state interactions over the entire range of temperatures and compare theory with experiment. The result shows that this broad range of phenomena can be accommodated within the BCS-Leggett description of BCS-BEC crossover.