In these lecture notes of the Summer School “Quantum coherence in solid-state systems”, I will present in a pedagogical way an overview of recent advances on the physics of polariton excitations in semiconductor microcavities in the strong light-matter coupling regime and I will discuss how the control of their dynamics can provide interesting quantum phenomena and devices with peculiar properties. In particular, I will present two different types of cavity polariton excitations, originating from two different optically active electronic transitions: i) exciton transitions in undoped quantum wells; ii) intersubband transitions in doped quantum wells containing a dense two-dimensional electron gas. I will draw the fundamental analogies and differences between these two types of polaritons. Concerning exciton-polaritons, I will explain how polariton-polariton phase-coherent interactions have been exploited for the experimental realization of micro-optical parametric amplifiers and for the generation of quantum correlated twin photon beams. The same kind of interactions is shown to lead to quantum fluid propagation properties. Concerning intersubband cavity polaritons, I will discuss: a) the essential features of the peculiar ultrastrong coupling regime and quantum vacuum radiation phenomena; b) very recent advances on electrically driven intersubband polariton devices emitting in the mid and far infrared; c) the possibility of lasing without population inversion based on stimulated scattering. In these lecture notes, accompanied by a comprehensive bibliography, the degree of technicality is reduced as much as possible in order to focus on the key physical issues, whose qualitative and intuitive aspects are discussed in detail.