This chapter discusses the techniques of complex modulation and demodulation through an intuitive approach. Modulation as a process in which data is mapped into symbols. The use of modulation constellations leads the problem of avoiding intersymbol interference, or the avoidance of symbols overlapping one another in time. The raised cosine filter is introduced as the solution, which have been plotted for several roll-off factors. The combined transmitter and receiver affects of the raised cosine filter are shown, leading to use of the square root of raised cosine filter.