The need for higher performance clocks, especially in defense, has driven the development of new frequency sources. Both microwave and optical technologies push to lower size, weight, and power while striving for GPS level performance or better. To improve legacy commercial microwave clocks, techniques such as laser cooling, trapping, and coherent population trapping are often employed. Transitioning these techniques from high-performance laboratory systems like fountain clocks to portable devices is starting to see some success. Optical clock technologies derive better performance by accessing narrow-line width, high-energy atomic states, but depend on frequency comb technology to interface with real-world systems. The basis for these clocks can range from vapor cells to optical lattices and trapped ions. Recent strides in hardware and techniques for both the frequency source and comb have led to investment by industry to transition the technology commercially. Applications for the new clock technologies include cyber, security, radar systems, communications, time-transfer, distributed networks, and more.