Achieving high performance is one of the most difficult challenges in designing digital circuits. Flip-flops and adders are key blocks in most digital systems and must therefore be designed to yield highest performance. In this book, a new high performance serial adder is developed while power consumption is attained. Also, a statistical framework for the design of flip-flops is introduced that ensures that such sequential circuits meet timing yield under performance criteria. Firstly, a high performance serial adder is developed based on the idea of having a constant delay for the addition of two operands. While conventional adders exhibit logarithmic delay. Also the proposed adder exhibits less area and power consumption. Secondly, a statistical framework for the design of flip-flops under process variations is presented in order to maximize their timing yield. In nanometer CMOS technologies, process variations significantly impact the timing performance of sequential circuits which may eventually cause their malfunction. Therefore, developing a framework for designing such circuits is inevitable.