We partition the communication signals into three – constellation, complex envelope (continuous I and Q baseband), and CW (real RF signal). Our focus in this chapter is on discrete-time representations, but we have to relate them to complex envelope and CW. This is done with binary cases – BPSK (2-PAM), OOK, and orthogonal (a form of FSK) using a rectangular pulse for converting to complex envelope and quadrature modulator to CW. Then binary modulations are extended to multi-level ones – PAM, QAM, and PSK. Additional topics that arise due to practical reasons are covered: offset QAM, scrambler, and 180° and 90° differential coding. PRS is an attempt to reduce the bandwidth. FSK is explored for noncoherent detection and its constant envelope property. The computation of PSD is explored analytically as well as numerically. Numerical simulation method is universally applicable even when no analytical solution is available. List of sections in Chap. 2Constellation, Complex Envelope, and CWPower of Digitally Modulated Signals and SNRMAP and ML DetectorsPAM, QAM, and PSKBER and Different Forms of SNROffset QAM (or Staggered QAM)Digital Processing and Spectrum ShapingFrequency Modulation – FSK, MSK, and CPFSKPSD of Digitally Modulated SignalsChapter Summary and References