In this talk low energy digital signal processing will be addressed. It will be taken from the angle of the power supply voltage. Do we need to lower the supply voltage? How low can we go? Is it energy efficient to go as low as possible? These are the type of questions that will be discussed. Design examples both from open literature as from own research will be given. Also a short excursion towards low energy SRAM memory, and its supply voltage, will be made.