A sensing system for determining the location and orientation of an object which comprises a magnetic tag. The sensing system comprises selection coils and interrogation coils. The selection coils are arranged to generate a spatially-varying DC magnetic field from which the location of the tag can be determined in use. At least some of the interrogation coils are arranged to generate one or more AC magnetic fields and at least some of the interrogation coils are arranged to receive harmonics, intermodulation products or time dependent variations of the AC magnetic fields, from which the orientation of the tag is determined in use.