This chapter addresses the propagation of harmonic distortion in meshed power systems with significant number of underground cables. Parts of the first objective are addressed in this chapter. It begins with a review of common network modelling principles for meshed systems. The standing wave behaviour in the passive network and the effects of harmonic sources on harmonic distribution in the passive grid are then investigated, and definitions of harmonic propagation and harmonic amplification are established. The evaluation of data presentation methods and the importance of predicting harmonics due to future grid expansions are explored. A practical case study on the Danish transmission system reveals the limitations of using transfer gain factors for predicting harmonic amplification in meshed grids. The chapter also introduces a benchmark model to examine standing wave phenomena and the impact of line configurations on harmonic voltages. The behaviour of harmonic sources is analysed, focusing on the influence of source phase angles on standing wave phenomena.