In non-sinusoidal and unbalanced systems, the definitions of apparent power and its power resolutions are still a topic that remained controversial in electrical engineering community. Thus, the various definitions were proposed in the literature, and different ones are encouraged by the standards focussed on power measurement. In addition, the guidelines and standards on the limitation of harmonic pollution do not include any method to determine the harmonic-producing consumers, and the conventional harmonic-pollution metering index as current total harmonic distortion is not capable of metering consumer's harmonic-pollution responsibility due to the fact that it depends on the distortion of utility side's supply voltage. Therefore, to fulfil this gap, for the harmonic-source detection and sharing harmonic responsibility between utility and consumer sides, several methods and indices are proposed in the literature. In this chapter, both frequency-domain power theory and harmonic-pollution metering approaches are summarized, and they are qualitatively and quantitatively analysed to clearly show their principles, limits, advantages and disadvantages.