A referendum on one of the country's opt-outs from the European Union was held in Denmark on 3 December 2015.

Specifically, the referendum was on whether to convert Denmark's current full opt-out on home and justice matters into an opt-out with case-by-case opt-in similar to those held by Ireland and the United Kingdom.

After Danish voters rejected the Maastricht Treaty in a 1992 referendum, the Edinburgh Agreement that was reached granted four exceptions to Denmark, one of which concerning Justice and Home Affairs.

When it became clear that, under new rules, Denmark would have to leave Europol due to its full opt-out, the two main political parties agreed to hold a referendum after the 2015 general election.

The second Lars Løkke Rasmussen government that was formed following the election subsequently decided on 21 August 2015 to hold a referendum on 3 December.