This chapter introduces the background and motivation of the research, emphasizing the growing need for advancements in probabilistic harmonic estimation and forecasting within power systems. It addresses the significant challenges associated with harmonic modeling and underlines the importance of resolving these issues to enhance system efficiency and reliability. A comprehensive review of existing work in the field is provided, covering both deterministic and probabilistic approaches, and exploring the integration of artificial intelligence in harmonic analysis. The chapter also discusses the practical challenges encountered in industrial applications of harmonic modeling. The research objectives and the contributions of the study are clearly outlined, setting the stage for the original insights and methodologies that differentiate this work from prior studies. The chapter concludes with an overview of the structure of the thesis, outlining the forthcoming in-depth discussions and analyses.