<p>Adaptive radiation is a pivotal driver of macroevolution, substantially contributing to the diversity of life by promoting rapid phenotypic and ecological adaptations. In birds, neoavian species account for over 95% of modern avian diversity, emerging from an explosive radiation event near the Cretaceous–Palaeogene boundary. In this Review, we explore the current challenges in resolving the avian tree of life and examine the key drivers of their radiation. We discuss the emerging consensus from phylogenomic studies using whole-genome data to illuminate the early diversification of Neoaves. Additionally, we discuss how the radiation of birds has influenced their diversity, emphasizing the interconnected macroevolution of phenotypic traits and genomic characteristics. Finally, we discuss the multiple impacts of climate change on bird populations, highlighting how evolutionary history informs and enhances our understanding of avian resilience to environmental change. This Review underscores the critical importance of integrating genomic data with trait-based analysis to explore unresolved questions pertaining to the adaptive radiation of birds, and sets the stage for future research on how contemporary ecological pressures might continue to shape avian diversity.</p>