We present dust polarization observations from filamentary IRDCs to star-forming cores. Single-dish observations show B-field structures perpendicular to the filament axis.The B-field is resolved in cores with ALMA in B6 towards W51, revealing satellite cores, locally pinched B-fields and a field in between cores that indicates a global drag towards the overall center of mass. Besides textbook cases, we present statistical results from a 50-source sample that shows generic field features and a systematically varying importance of the B-field versus gravity.