This book offers a comprehensive and interdisciplinary examination of how complexity emerges, transforms, and accelerates across the entire 13.8-billion-year history of the Universe. It brings together chapters from leading researchers to explore the deep structure of complexity-from cosmic origins and planetary evolution to biological innovation, human development, civilizational dynamics, and possible future trajectories. Notably, several chapters bridge multiple phases of Big History, providing valuable cross-disciplinary insights-such as comparisons between cosmic and terrestrial evolution and analyses of energy dissipation across physical and complex adaptive systems. This book offers a comprehensive exploration of complexity&s manifestations and transformations across time and scale. By exploring these diverse topics, the book contributes to the broader field of Big History, deepening our understanding of complexity&s interconnected nature across the cosmos, life, and human civilization.