This book addresses the intricate challenges posed by the development of shale gas in nanoporous shale formations. By seamlessly integrating molecular simulation with mathematical modeling, the authors delve into the microscopic behavior of shale gas, particularly focusing on its occurrence, diffusion, and flow mechanisms.One of the key contributions of this book is the introduction of the concept of "wall-associated diffusion". This concept offers a fresh perspective on the intricate interaction between gas molecules and pore walls, providing deeper insights into how these interactions shape the overall flow characteristics.Furthermore, the authors propose a unified flow model that takes into account various flow regimes, providing a more comprehensive understanding of the complex flow behavior in shale gas reservoirs. This model not only enhances our theoretical knowledge but also has practical implications for optimizing shale gas extraction.The findings presented in this book offer valuable insights for improving shale gas extraction techniques and enhancing our understanding of unconventional oil and gas resources.