  The interstellar medium (ISM) is constantly evolving due to unremitting
injection of energy in various forms. Energetic radiation transfers energy to
the ISM: from the UV photons, emitted by the massive stars, to X- and
$\gamma$-ray ones. Cosmic rays are another source of energy. Finally,
mechanical energy is injected through shocks or turbulence. Shocks are
ubiquitous in the interstellar medium of galaxies. They are associated to star
formation (through jets and bipolar outflows), life (via stellar winds), and
death (in AGB stellar winds or supernovae explosion). The dynamical processes
leading to the formation of molecular clouds also generate shocks where flows
of interstellar matter collide. Because of their ubiquity, the study of
interstellar shocks is also a useful probe to the other mechanisms of energy
injection in the ISM. This study must be conducted in order to understand the
evolution of the ISM as a whole, and to address various questions: what is the
peculiar chemistry associated to shocks, and what is their contribution to the
cycle of matter in galaxies ? What is the energetic impact of shocks on their
surroundings on various scales, and hence what is the feedback of stars on the
galaxies ? What are the scenarios of star formation, whether this star
formation leads to the propagation of shocks, or whether it is triggered by
shock propagation ? What is the role of shocks in the acceleration of cosmic
rays ? Can they shed light on their composition and diffusion processes ? In
order to progress on these questions, it is paramount to interpret the most
precise observations with the most precise models of shocks. From the
observational point of view, the James Webb Space Telescope represents a
powerful tool to better address the above questions, as it will allow to
observe numerous shock tracers in the infrared range at an unprecedented
spatial and spectral resolution.
