Optical dating, also called Optically Stimulated Luminescence dating, is a powerful emerging technique for determining sedimentary ages of geologically young materials and studying the processes that shape the Earth's surface. The technique is developed on principles of solid state radiation dosimetry and bridges a significant temporal gap among isotopic-decay-based dating methods. This presentation will review the relevant dosimetry concepts and describe how they are used to construct a geologic clock. A specific example from Chaco Culture National Historic Park will be presented to demonstrate how and why geologists use this dating method and finally some unresolved basic research issues will be discussed.