The book adopts a multiscale theoretical framework to systematically address localized deformation in plastic geomaterials. It integrates experimental findings with advanced numerical methods, including discrete element simulations and finite element modeling using higher-order continuum theories, providing a comprehensive understanding from micro- to macroscale perspectives. The book will provide insights into the nuances of strain localization that traditional modeling often overlooks, thereby enhancing predictive accuracy and model fidelity. The book is designed for graduate students, researchers, and professionals in geotechnical engineering, materials science, and related fields who have a solid grounding in continuum mechanics and numerical methods. It is also suitable for readers seeking an advanced, research-focused perspective on multiscale modeling.