Modern wireless communications are based on the exploitation of channel behavior and/or user requirements by adapting one or more transmission parameters. Amongst several systems the OFDMA offers a lot of capabilities to the system designer allowing adapting in several ways the communications. This chapter deals with the introduction of the basic principle of an adaptive OFDMA system by focusing on those most important parameters that can be adjusted in order to have better performance. Finally, some techniques are presented also by showing some numerical results.