This paper addresses the question of why VSX word order is possible in Spanish but excluded in other Romance languages (Catalan and Italian). It aims at offering an overview of the properties of VSX in Spanish, as well as explaining how the availability of VSX depends on interface requirements on the mapping between syntactic structure and information structure. VSX is interpreted as a single informational unit, without internal partitions (topic-comment, focus-background); this typically results in a thetic, wide focus interpretation, related to a stage topic. Languages like Italian and Catalan reject the processing of marked orders as non-partitioned units, which rules out VSX. More permissive languages, like Spanish, allow for the absence of partitions in marked orders.