Abstract Icelandic and German differ in the head-complement order (VO vs. OV), but their morpho-syntactic systems of verbal and nominal inflection are similar enough for factoring out the specific grammatical effects of the OV/VO-property. The analysis of a broad range of constructions (quirky subjects, expletive subjects, object shift, scrambling, particle constructions, V-clustering) provides the empirical basis for the following claim: the headedness difference (OV vs. VO) is the basic and crucial factor for the systematic differences between the respective grammars. As for the theoretic modeling of the OV/VO property, the key concept is argued to be a universal constraint on the direction of merger interacting with the directionality of licensing by the head.