Three-phase systems are commonly used for generation, transmission and distribution of electrical power. This monograph is aimed to differentiate and explore the nature of total instantaneous power in a three-phase system as compared to single-phase system. The monograph includes analysis of three-phase instantaneous power with and without source inductances. Balanced as well as unbalanced loads have been considered for analysis. Modeling and simulation of electrical power system included in this monograph enhances and motivates researchers to conduct research investigations using MATLAB/Power System Blockset. The mathematical analysis included in this monograph may lead to innovative and novel ideas. Praise and glory to ALMIGHTY GOD for the successful compilation of this monograph.