The number of power electronic and distorting loads, continue to grow at a rapid pace. Accompanying this growth in distortion sources is an increased sensitivity of certain types of loads to harmonic distortion, and poor power quality in general. The result is greater variance in the value loads place on a harmonic free supply, and therefore what they are prepared to pay to mitigate the potential consequences of harmonic distortion. Harmonic distortion imposes costs worth considering, if not, no action would be taken by networks to mitigate the effects of harmonic injections. This thesis develops tools that allow the valuation of the harmonic injections made by loads throughout a network. The ability to accurately value harmonic distortion is critical if an optimal allocation of resources committed to the problem is to be achieved. Also this work develops methods by which an optimal allocation of resources can be brought about, and ways the costs of any action taken, can be distributed in a manner deemed fair. Marginal pricing is the technique used to achieve an efficient allocation of resources. In a decentralised framework, marginal pricing will encourage efficient behaviour from each network participant. This is achieved by making the cost of each load's actions transparent, and borne by that load. Also marginal pricing fully utilises all the available knowledge throughout the system. The utilisation of knowledge is the key to solving all economic problems, and the difficulty associated with gathering knowledge makes centralised decision making inherently inefficient. This thesis develops marginal prices for harmonic injections, and these prices are demonstrated to encourage efficient behaviour from each load with respect to reducing the injection they make into the system. It is also shown marginal pricing has the ability to encourage efficient allocation of filter resources. By determining exactly how much the distortion is worth, it is possible establish exactly how much the network is willing to pay, to reduce that distortion. There are multiple ways marginal pricing can be implemented, depending on whether charges are based on the Norton injections of each load or the total harmonic injection. The advantages and disadvantages of each method are discussed.