We have an active and diverse program to study the properties of molecular clouds and their connection with dense cores. Since molecular clouds provide the initial conditions for dense cores, it is important to determine some of their main properties: the amount of turbulence in the molecular cloud and inside dense cores, the amount of energy radiated by turbulent dissipation, and the role of magnetic fields. We have studied distant Infra-Red Dark Clouds (IRDCs) and nearby molecular clouds in dense gas tracers, using both single dish and interferometers, to reveal a large fraction of dense gas (as traced by NH3) present in the intra-core medium and to highlight the presence of subsonic turbulence inside dense cores even in the higher-mass star-forming regions traced by IRDCs. The relation between the kinematics and other physical properties of the dense cores and their parental molecular clouds has been explored. In addition, a systematic study of mid-J to high-J CO transitions in IRDCs provided a possible detection of the energy generated by turbulent dissipation. Finally, a comparison between Planck and polarization of background stars was carried out and it showed small differences between both techniques, confirming the validity of the Planck based polarization measurements in molecular clouds.