The divergent interpretations of data, the lack of common metadata and the absence of universal reference data hinder governments from seamless data exchange, information systems integration and the delivery of cross-border public services. To overcome this, governments develop e-Government metadata repositories to store reusable data models, schemata, taxonomies and codelists. We use the term semantic interoperability asset to refer to these types of resources. These repositories however differ in their scope, target group, implementation technologies and end-user interfaces. Although, the semantic content they include can often be reused, even bypass the domain it was originally designed for, their physical isolation and the heterogeneity of the assets' descriptions hamper the reusability of common concepts and cross-repository search. To deal with these challenges, this paper introduces the Asset Description Metadata Schema, an initiative of the ISA programme of the European Commission, which aims to deliver a common metamodel for semantic interoperability assets.