The phase is the other side of the coin when speaking transfer functions, with the first side being the magnitude. The phase is extremely important because—and in conjunction with the magnitude—it explains to us how the system is responding. Whether the system is stable, unstable, capacitive dominated, inductive dominated, or flat resistance dominated, the phase shows it. The phase ties in very nicely with the presence of poles and zeroes; each contributes a − 90deg or + 90deg to the phase, respectively. Also the order of the pole and/or zero gets reflected in the phase. Finally the phase is the only discerning knob in differentiating two systems with identical magnitude plot but nonetheless different response. This chapter and the chapter problems give a good starting point how to interpret the phase, and the rest of the text regurgitates the same concept.