Epitaxial growth of thin films is, in general, based on specific interfacial structures defined by a minimum of interfacial energy and usually influenced by the structural mismatch. In the present study, the structures and energies of (0001) InN/GaN epitaxial interfaces are studied using the Tersoff interatomic potential. The potential describes the metallic and intermetallic interactions sufficiently well and is assembled in order to accurately reproduce the lattice and elastic parameters of wurtzite Ga(In)-Nitrides. Different configurations are examined for each interface depending on polarity and atomic stacking. It is shown that the interfacial structures of InN thin films grown with indium polarity interfaces exhibit lower self-energies than those of N-polarity. Although the substrate and the epilayer were assumed to exhibit the wurtzite crystal structure, both wurtzite and zinc-blende type atomic stackings are possible at the interfacial region since they were found energetically degenerate within the accuracy of our model. Finally, the spatial location of the epitaxial interface is also energetically defined. Epitaxial interfaces in this system can in principle be imagined to pass through so-called single or double atomic bonds, but the former case was energetically more favourable.