The interstellar medium deals with complex chemical processes, involving molecular species and dust particles. Carbon chains formation and chemical bistability have been investigated.

How non thermal energy inhibits the growth of gravitational instability.

Many of the theoretical and observational activities in our laboratory therefore focus on the physics of interstellar matter and star formation.

The interstellar diffuse medium in the pressure conditions prevailing in our Galaxy is thermally bistable and turbulent.

Disentangling the contribution of each of the phases to the energy budget of the medium is made possible in external galaxies for which global measurements can be achieved.

Studies of diffuse gas at cosmological distances have been performed by analysing the UV spectra of quasars and deep high resolution images of quasar fields obtained with the Hubble Space Telescope spectra.

There is little doubt that the magnetic field plays a major role in the formation, evolution and structure of many astrophysical and geophysical objects like galaxies, molecular clouds, accretion disks, stars and planets. As such, magnetic field has received considerable attention during the last decades. However in spite of these efforts, many questions remain largely open from astrophysical and geophysical points of view, on theoretical and numerical grounds. This is largely due to the inherent complexity of the non-linear magnetic processes as magnetohydrodynamic (MHD) turbulence and dynamo, to the uncertainties regarding the validity of the ideal MHD approximation and to the difficulty in computing MHD flows.