The last few years have seen the emergence of a variety of quantum phenomena specifically related to electronic or optical confinement at a sub-wavelength scale. Rapid developments occurred simultaneously in atomic physics (especially in cavity quantum electrodynamics) and in solid state physics (advances in quantum well technology and nano-optoelectronics). Breakthroughs in near-field optics provided new tools that could be applied to these domains. But the key concepts used to describe these effects are often very different, being specific to the community involved in a particular development. Readers of this work are given the opportunity to deepen their understanding of advances related more or less to their own field, while the basic concepts of the different fields are presented by means of tutorial introductions.