This work reviews some of the results achieved at CNR-IMM in the last years on nanoscale probing of interfaces in gallium nitride (GaN) for devices applications. A special emphasis will be given to the insights obtained using high resolution techniques based on scanning probe microscopy (SPM), often employed in combination with conventional macroscopic measurements. Some aspects related to GaN interfaces that are relevant for devices technology, ie Schottky and Ohmic contacts, will be discussed as examples.