Dengue virus (DENV) is a rapidly evolving arbovirus responsible for significant morbidity and mortality worldwide. Understanding its evolutionary trajectory is essential for tracking viral emergence, transmission dynamics, and the factors driving its geographic expansion. This chapter provides a comprehensive overview of the genetic diversification and phylogenetic pathways of DENV, focusing on serotype evolution and the classification of genetic lineages. We discuss molecular phylogenetics as a key tool for elucidating the evolutionary relationships among DENV strains and highlight the application of phylodynamic approaches to infer viral dispersal patterns in endemic and newly affected regions. Furthermore, we examine the historical spread of DENV, with particular attention to cross-border transmission events facilitated by human mobility and trade. Additionally, we explore the role of climatic and ecological drivers, such as temperature fluctuations, vector adaptation, and urbanization, in shaping the evolutionary dynamics of the virus. By integrating genomic, epidemiological, and ecological data, this chapter underscores the importance of a multidisciplinary approach to dengue surveillance and control, ultimately contributing to the refinement of predictive models and public health interventions aimed at mitigating the impact of DENV outbreaks.