Massive, cold, dense filaments, often appearing as infrared dark clouds (IRDCs), are the nurseries of massive stars. No measurements of magnetic fields in IRDCs in a state prior to the onset of high-mass star formation (HMSF) have previously been available, and prevailing HMSF theories do not consider strong magnetic fields.Our recent polarization observations show that massive filaments are strongly magnetized and that the strong magnetic field is as important as turbulence and gravity for HMSF. Our next step is to understand whether magnetic field continues to play a dominant role in filaments as cores within such IRDCs collapse and form clusters. To do this we are conducting dust polarization observations. Combining near-infrared, far-infrared (SOFIA HAWC+) and submm dust (APEX, ALMA) polarization, we study how the magnetic field evolves and interacts with the larger scale field of the ISM. Providing a detailed case study of a nearby low-mass star forming IRDC, I will present results of the POLSTAR survey focused on understanding the role of magnetic fields in IRDCs that are at different stages of evolution.