The term modulation denotes the process of transforming the information generated by a source into a signal that is suitable for transmission over a physical channel, in order to convey it to a receiver. When the information is represented by a sequence of bits, {b_l}, we talk of digital modulation. The binary sequence detected by the receiver, {c_l}, may well be affected by errors, i.e. c_l ~= b_l for some values of l, due to distortion and noise introduced by the transmission medium. In this chapter we present a survey of the main modulation techniques used in modern digital communication systems (e.g., PAM, PSK, QAM, etc.). The performance of each modulation/demodulation method is evaluated with reference to the bit error probability, Pbit = P[c_l ~= b_l], and a comparison of the various approaches is given.