It was realized soon after interstellar polarization was first detected in 1949, that the effect was caused by an interaction between the dust and magnetic field in the interstellar medium. Over the following decades significant theoretical progress has been made in understanding the alignment mechanism, with the current consensus favoring alignment by direct radiative torques. However, little direct observational evidence has been available to constrain the details of the grain alignment.

We have recently used multi-band optical, and NIR, polarimetry towards six nearby clouds, supported by optical, NIR and FIR photometry, to show that the grain alignment is indeed driven by radiative processes. Our data also show a strong impact of the local star formation on the polarization, including possible alignment damping due to the X-ray field from embedded YSOs. A quantitative understanding of interstellar grain alignment promises to allow new probes of the grain micro physics and to put the potentially powerful diagnostics of the magnetic field available through optical/NIR and FIR polarimetry on a secure footing.