This thesis presents details on the design, construction, and characterization of a novel compact optical clock based on a two-photon transition in calcium. Optical atomic clocks have reached unprecedented accuracy and precision and have the potential to revolutionize metrology. However, many of the applications of optical clocks, such as the detection of dark matter and gravitational waves, deep space navigation, measurements of variations in fundamental constants, and precision geodetic measurements, require compact portable clocks. Building optical atomic clocks on a scale suitable for most field applications is an ongoing challenge in the precision metrology community. This work describes a clock that can be made smaller and simpler than most existing optical clocks, while still operating with state-of-the-art precision. The basis for these improvements is using a two-photon transition, which eliminates the need for sub-Doppler cooling and tight confinement of the atoms. The design for the calcium two-photon clock is given, and the construction of the clock components is described. Experimental results are presented for the search for the clock transition frequency, which has never before been precisely determined. A detailed uncertainty budget is given, showing that this clock should be able to achieve a fractional frequency uncertainty of
∼10−17. In addition, a novel technique of ``magic polarization'' is presented which can be implemented to mitigate probe laser light shifts, long thought to be a serious impediment to precision two-photon clocks. An experiment in which a two-photon clock based on rubidium was launched and operated on a stratospheric balloon and subsequently recovered is also described. This work represents an advancement in the development of compact portable optical clocks which will further push the boundaries of precision measurement and our understanding of the universe.