This chapter complements the Specification of Harmonic Requirements and Equipment for HVDC Converter Stations chapter, which dealt with the technical specification aspect of HVDC harmonics and filtering, and leads on to an examination of how such topics are studied and how mitigation methods, such as filters, are designed. The chapter is restricted to the AC side of the HVDC converter, with similar aspects for the DC side being dealt with in Chap. 28, “DC Side Harmonics and Filters for LCC and VSC HVDC Converter Stations.” Both line commutated (LCC) and voltage sourced (VSC) HVDC converters are considered. The starting point of all such design studies is to calculate the harmonic generation by the converter, which for LCC is extremely significant, but for VSC is very much smaller. Modeling of all aspects of the HVDC station and the connected network at harmonic frequencies is then discussed. The techniques of filter design are described, with guidance regarding the most appropriate types and how practical considerations such as tolerances and deviations in network frequency may be taken into account. Issues regarding the stability of the interaction at harmonic frequencies between the HVDC control system and the AC network are analysed – this being of particular relevance for VSCs. The cross-modulation phenomenon of interaction between AC and DC side harmonic distortion, and its various implications are also discussed. Finally, the chapter examines how to verify that the design of mitigation is adequate and that the resulting performance in the field is compliant with the specification.