Public and private organizations increasingly release their data to gain benefits such as transparency and economic growth. The use of these open data can be supported and stimulated by providing considerable metadata (data about the data), including discovery, contextual and detailed metadata. In this paper we argue that metadata are key enablers for the effective use of Linked Open Data (LOD). We illustrate the potential of metadata by 1) presenting an overview of advantages and disadvantages of metadata derived from literature, 2) presenting metadata requirements for LOD architectures derived from literature, workshops and a questionnaire, 3) describing a LOD metadata architecture that meets the requirements and 4) showing examples of the application of this architecture in the ENGAGE project. The paper shows that using metadata with the appropriate metadata architecture can yield considerable benefits for LOD publication and use, including improving find ability, accessibility, storing, preservation, analysing, comparing, reproducing, finding inconsistencies, correct interpretation, visualizing, linking data, assessing and ranking the quality of data and avoiding unnecessary duplication of data. The Common European Research Information Format (CERIF) can be used to build the metadata architecture and achieve the advantages.