A technique for real-time formation of optimal power spectral density masks is disclosed. In one particular exemplary embodiment, the technique may be realized as a method for real-time formation of optimal power spectral density masks. The method may comprise sensing line conditions in a communication medium, wherein the communication medium is capable of carrying signals in a plurality of tones. The method may also comprise determining, in real-time, one or more power spectral density masks that substantially optimize transmissions of the signals in the plurality of tones. The method may further comprise transmitting the signals in the plurality of tones based on the one or more power spectral masks.