Understanding how stars form is central to astrophysics. Low mass stars, like our Sun, may host planets where life could emerge, and the most massive stars govern the physics and the chemical enrichment of the interstellar medium of galaxies. Molecular filaments have been recently identified as the main sites of star formation. My main research is thus to derive a consistent scenario for the formation of these filaments and study their fragmentation into star forming dense cores. For that, I use various observational tracers of dust and gas, in total and polarized emission, to investigate the role of the main physical processes (turbulence, gravity, magnetic field) at play in the interstellar medium. The observational data that I use are obtained with space and ground-based facilities such as the Herschel, Planck, APEX, IRAM-30m, Nobeyama-45m, ALMA, and JCMT telescopes. In parallel, I work with theorists to confront observational results with numerical simulations and theoretical models.