In Chap.  3 , the PML medium matched to a vacuum has been introduced in time domain ( 3.1 ), from which the frequency domain equations ( 3.5 ) were derived. The PML ( 3.1 ) is known as the split PML. In the present chapter, it is shown that other time domain equations can be derived from ( 3.5 ), which yields other time domain PMLs matched to a vacuum, to lossy media, to anisotropic media, and to dispersive media.