As discussed in the first chapter of this book, the first step in obtaining constant DC voltage out of the grid voltage is rectification. That will be our fist subject in this chapter. Two types of rectification will be considered. The first, named half-wave rectification, is simply “deleting” one half-period of the mains current and delivers only the other half to the load. So we get a periodic pulse train of halves of a sinusoid. In many applications, this is considered inefficient and full-wave rectification is implemented. Now, both halves of the grid sinusoid are used with the fact that one of them gets the sign changed. The load is now getting two halves of the sinusoid with the same sign which, normally, doubles the voltage and the power delivered to it. Also, two types of components will be used in the rectifier circuits: the rectifying diode and the silicon controlled rectifier (SCR). The waveform so obtained may be immediately useful for power applications where the presence of harmonics is of no significance. When an electronic system is to be supplied, however, one would need a supply voltage of constant value in time, i.e., with harmonics eliminated. That is usually achieved by filtering the rectified signal. Several types of filters will be considered here with rising complexity. Circuit analysis will be performed and efficiency of harmonic elimination (often called selectivity) will be established for each one of them. The influence of the harmonics (generated within the rectifier) to the grid current (usually named electromagnetic interference) will be considered briefly, too. Especially, the term power factor will be introduced and procedures for estimation of its value will be recommended.