This paper begins with a brief overview of some basic concepts in clock based design, and a brief overview of the traditional role of CTS within digital design flows. It then explains why and by how much design timing is diverging around CTS. The concept of clock concurrent optimization is then introduced and its key defining features outlined. The paper concludes with a summary of the key benefits of clock concurrent optimization and an explanation of why it comprehensively addresses the divergence in design timing around CTS.