  Local constitutive relations, i.e. a weak spatial dispersion, are usually
considered in the effective description of metamaterials. However, they are
often insufficient and effects due to a nonlocality, i.e. a strong spatial
dispersion, are encountered. Recently (K.~Mnasri et al., arXiv:1705.10969), a
generic form for a nonlocal constitutive relation has been introduced that
could accurately describe the bulk properties of a metamaterial in terms of a
dispersion relation. However, the description of functional devices made from
such nonlocal metamaterials also requires the identification of suitable
interface conditions. In this contribution, we derive the interface conditions
for such nonlocal metamaterials.
