The last five years have seen increasing amounts of open data being published on the Web. In particular, governments have made data available across a wide range of sectors: spending, crime and justice, education, health, transport, geospatial, environmental and much more. The data has been published in a variety of formats and has been reused with varying degrees of success. Commercial organisations have begun to exploit this resource and in some cases elected to release their own open data. Only a relatively small amount of the data published has been linked data. However, the methods and techniques of the semantic web could significantly enhance the value and utility of open data. What are the obstacles and challenges that prevent the routine publication of these resources as semantically enriched open data? What can be done to improve the situation? Where are the examples of the successful publication and exploitation of semantically enriched content? What lessons should we draw for the future?