The purpose of this essay is twofold: first, to examine the nature of the European Union’s system of governance; and second, to investigate the implications of the EU’s institutional and decision-making arrangements for sovereignty. To this end, it engages a set of theories of European integration applied to a selection of developments of contemporary EU integration that have had different effects on EU Member States’ sovereignty. The essay attempts to highlight the linkages between these theories to show how the current EU political organization of authority qualifies as “shared sovereignty” in practice. In doing so, it reviews the pillar theories of integration; explores the concepts of “integration” and “sovereignty”; and presents three levels of development that are used to frame wider and deeper integration and its effects on Member States resulting in the transfer and sharing of sovereignty.