In this article, the so-called wh-relative clause construction is investigated. The German wh-relative clauses are syntactically relevant as they show both, root clause and subordinate clause properties. They matter semantically because they are introduced by a wh-anaphor that has to be resolved by an appropriate abstract entity of the matrix clause. Additionally, the wh-relative clause construction is discourse-functionally peculiar since it evokes coherence. Besides these interesting empirical characteristics, whrelatives raise important theoretical questions. It is argued that the standard HPSG theory has to be extended to account for non-restrictive relative clauses in general, and to cope with the particular properties of the wh-relative construction.