This lecture introduces the principles and foundations of synchronous RTL design, focusing on the design of custom digital circuits, implementing algorithms with registers and logic, and the design process visualized by the Y-Diagram. It clarifies the concept of 'Synchronous Register Transfer Level (RTL) Design' as an intermediate representation between behavioral and structural perspectives, emphasizing the importance of block diagrams, signal classes in synchronous design, and managing structural complexity with hierarchy. The lecture also covers common complex components, RTL design abstraction, and famous examples of synchronous design, such as counters with reset. It concludes with a discussion on forbidden RTL design examples.