This book presents select proceedings of the 4th International Conference on Applied Mathematics in Science and Engineering (AMSE-2025). It addresses the latest research and advancements in Nonlinear Dynamics and Partial Differential Equations (PDEs) in Applied Mathematics. Nonlinear dynamics play a crucial role in understanding and solving complex natural and technological phenomena, with its applications in PDEs remaining a rapidly evolving field. Featuring contributions from leading experts, this book provides an in-depth exploration of nonlinear dynamical systems, emphasizing their applications in analyzing, modeling, and solving PDEs across different disciplines. Covering a broad spectrum of topics, the book delves into theoretical foundations, numerical techniques, and real-world applications. Key themes include multi-faceted applications of fundamental laws & analytical/numerical methods of applied mathematics. Designed for researchers, advanced students, and professionals, this book provides a comprehensive resource by bridging theory and application, inspires further investigation, promotes interdisciplinary collaboration, and makes substantial contributions to the advancement of knowledge.