This paper reviews the inherent change in the observed mechanical behavior of electronic components, structures, and multimaterials as a result of the ongoing miniaturization. In general, the size of microstructures is no longer negligible with respect to the component size in micro and submicron applications. Additionally, surface layers start to play a more prominent role in the mechanical response. Microstructural effects, macroscopically triggered gradient effects, and surface effects jointly appear and constitute the various size effects that can be observed. Classical continuum mechanics theories fail to describe these phenomena, and higher-order multiscale theories are required to arrive at an appropriate prediction of the mechanical behavior of miniaturized structures.