This chapter explores how the approach that follows the complex systems theory can offer a transformative lens and a shifting action for understanding and designing future communication infrastructures, not only in the transition toward 6G but also beyond. By integrating insights from network science and data science, evolutionary game theory, machine learning, collective dynamics, and multiplex and hypergraph modeling, it will be discussed a novel conceptual and analytical roadmap for managing the ever-increasing dynamism, heterogeneity, and intelligence of modern communication ecosystems.