This book serves as a definitive guide for designers and product leaders navigating the challenges of creating user experiences for large-scale, data-intensive, and intelligent systems. It moves beyond standard interface design to address the complexity inherent in enterprise software, big data visualization, and automated workflows. Readers will learn practical frameworks for managing cognitive load, designing for collaboration, and orchestrating complex processes at scale. Furthermore, it provides essential strategies for integrating AI features, focusing on critical issues like trust, transparency (XAI), and ethical design, to ensure that intricate systems remain intuitive, accountable, and fundamentally human-centered.