I will first review the familiar coupled mode theory, and then apply it to some simple cases: coupled quantum wells, the waveguide coupler, the slot waveguide, the long-range plasmonic surface wave, an LC-oscillator coupled to a transmission line, an atom in a small cavity, the dressed atom and laser trapping, entanglement, and finally, as an example of irreversible process, an oscillator coupled to a continuum of modes.  A Leitmotiv in the talk is the obvious but often forgotten fact that a normal mode of an isolated component system is not a normal mode of the coupled system.

*On leave from University of Maryland, College Park, USA