This lecture explores diagrid structural systems in contemporary tall buildings, focusing on how diagonal grid frameworks replace conventional rectilinear structural systems. It explains the principles of triangulation, structural efficiency, and load distribution, showing how diagrid structures improve stiffness, reduce the need for vertical columns, and enable flexible architectural forms. The lecture also presents notable examples such as The Gherkin, Hearst Tower, and CCTV Headquarters, demonstrating how diagrid systems integrate engineering innovation with expressive architectural design.