The paper investigates head final effects (HF-effects) in German and English and argues that the syntactic configuration that underlies them gives rise to three different types of violations in the interfaces. It is shown that HF-effects are either morphological or prosodic in nature. A diagnostics – morphological versus syntactic displacement – is established that allows to connect HF-effects to their relevant interface conditions. The prosodic conditions on word order are then argued to be twofold: they involve a condition on heavy constituents, on the one hand, and a condition on the mapping of syntactic constituents onto prosodic constituents respecting the Strict Layer Hypothesis, on the other hand. Finally, I argue that a pure syntact...