Multiple physical phenomena can be modified in vicinity of metamaterials or sometimes much simpler systems, like metallic films. While control of spontaneous emission is arguably the most studied case, other phenomena of interest include stimulated emission, Förster energy transfer, van der Waals interactions, and even chemical reactions. Some of these processes occur in the regime of weak coupling of molecular dipoles with nonlocal dielectric environments. They lead to change in the transition rates (e.g. rate of spontaneous emission in vicinity of hyperbolic matamaterials) but not energy eigen-values of interacting subsystems. The stronger coupling of molecules with their environments, e.g. localized or propagating surface plasmons or cavities, results in modification of the eigen-states of the coupled systems and the normal mode splitting (or Rabi splitting) of the corresponding dispersion curves. Of particular interest, are the strongly couples systems involving large ensembles of highly concentrated molecules or quantum dots. In this case, the mode splitting and the corresponding energy eigen-values can be of the order of 1 eV ! (the regime of ultra-strong coupling). Such gigantic alteration of the energy states, comparable with those of non-interacting constituents, can completely change the energy landscape of many physical and chemical processes, leading to ultimate control of matter with light or even vacuum fluctuations. The examples of these processes and their qualitative interpretation will be discussed in the presentation.