This open access book provides a deep dive into the digitalization and intelligent technologies transforming the field of aircraft engines, offering insights into their critical importance and the challenges they aim to address. As the aerospace industry faces increasing demands for efficiency, sustainability, and innovation, digital and intelligent technologies have become essential tools in advancing aircraft engine design, performance optimization, and lifecycle management. These technologies are reshaping the way engines are developed and maintained, enabling breakthroughs in predictive maintenance, real-time diagnostics, and cross-disciplinary collaboration. However, achieving these advancements comes with significant challenges, such as data integration, simulation accuracy, and the need for seamless coordination among multiple disciplines. This book begins by examining the current state of digital engine technologies, highlighting their role in improving design efficiency, operational safety, and cost-effectiveness. Through a detailed analysis, it identifies critical obstacles, such as the complexity of integrating heterogeneous data, achieving high-fidelity simulations, and optimizing whole-system performance in multi-disciplinary contexts. Moving beyond diagnostics, the text explores innovative approaches like digital twin-based simulation modeling, which combines physical models with real-world data to accurately predict engine behavior. It also introduces advanced methods for creating enhanced whole-engine system models, enabling multi-disciplinary collaboration to ensure design reliability and efficiency. A significant portion of this book is dedicated to the concept of the digital thread, a framework that ensures consistent data integration and automated workflows throughout the engine lifecycle. By leveraging digital threads, engineers can streamline design iterations, reduce uncertainties, and improve overall product quality.