Denmark obtained four opt-outs from the Maastricht Treaty following the treaty's initial rejection in a 1992 referendum.
The opt-outs are outlined in the Edinburgh Agreement and concern the Monetary Union (EMU), Common Security and Defence Policy (CSDP), Justice and Home Affairs (JHA) and the Citizenship of the European Union.
With these opt-outs, the Danes accepted the treaty in a second referendum held in 1993. In 2000, Danes rejected a referendum on adopting the euro.