Citizens and enterprises in the European Union benefit from a common internal market and other freedoms. The resulting and growing mobility and cross-border collaboration necessity leads to specific challenges for e-Government applications. This article presents the results of a study run by Luxembourg?s Presidency of the EU during the first half of 2005. This study investigated one central aspect in this area: How do countries identify their citizens and businesses, and what are their national provisions regarding data protection and privacy that limit and regulate the sharing of such data? In more technical terms: What is the impact of identity management and related privacy issues on the interoperability of e-Government systems? The status quo in 18 member states is illustrated, and compared with the results of a similar study run in 2001. We present a general model for describing the framework of identity management in cross-border contexts.