The development of nanometer-scale mechanical structures into sensitive and integrated devices has enabled us to envision applications such as cell phones the size of a wrist watch, fast and sensitive pathogen detectors, and ultra-sensitive field and force gauges. An exact understanding of the physical phenomena affecting NEMS behavior should aid in the successful application of these systems. Several important achievements in this field will be described - from fabrication of ultra-small and ultra-high frequency resonant structures in a variety of materials to understanding their behavior and improving their performance. Some of the topics to be discussed include the time scales of nanoscale dynamics, the operation of NEMS in vacuum and in air, the sources of energy dissipation, and the effects of thin film mechanics in NEMS.@footnote 1@ @FootnoteText@ @footnote 1@In collaboration with: M. Zalalutdinov, K. Aubin, A. T. Zehder, J. M. Parpia, and H. G. Craighead, Cornell Center for Materials Research, and J. E. Butler, Naval Research Labs.