In This book, special emphasis is placed on the interaction of X-ray polarised and non-polarised radiation with hexagonal BN (h-BN) crystal. h-BN is one of the most anisotropic layer compounds. Near the B and N K shell ionisation thresholds the dielectric tensor in h-BN demonstrates sharp variations with photon energy and results in intriguing optical properties of the compound. X-ray absorption near the thresholds is strongly influenced by the short range order parameters of the layers and demonstrates the pronounced "molecular" properties.