In this talk I will briefly review the basic principles of
electromagnetic field quantisation in the presence of macroscopic
matter, and explain its relevance to the quantum interaction between
(isolated) microscopic particles and macroscopic surfaces. As a first
example, I will review some aspects of propagation of nonclassical light
through absorbing optical devices. I will then concentrate on two
aspects of atom-surface interactions --- decoherence and dispersion
forces (Casimir, Casimir-Polder and van der Waals forces). Both effects
can be understood within the framework of macroscopic QED as spatially
dependent relaxation processes and line shift mechanisms, respectively.
I will present examples of highly excited atoms and weakly bound
molecules that are particularly susceptible to changes in dispersion forces.