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Atomic frequency standards are used to generate accurate and precise time and frequency, enabling many communications, synchronization, and navigation systems in modern life. GPS and other satellite navigation systems, voice and data telecommunications, and timestamping of financial transactions all rely on precise time and frequency enabled by atomic frequency standards. This review provides a snapshot and outlook of contemporary atomic frequency standards and the applications they enable. We provide a concise summary of the performance and physics of operation of current and future atomic frequency standards. Additionally, examples of emerging frequency standard technologies and prototype demonstrations are presented, with a focus on technologies expected to provide commercial or military utility within the next decade. We include a comparison of performance vs. size and power for current atomic frequency standards, and we compare early prototypes of next-generation frequency standards to current product trends. An empirical relationship between frequency standard performance and product size is developed and discussed. Finally, we provide a mapping between applications and frequency standard technologies.