The date has finally been announced for 23rd June.
Here are some background sources on the referendum and what is means.
David Cameron's statement to Parliament in 22nd February
Statement about the EU renegotiation and settlement on 20th February
Use the Uk Parliament website to terrace the passage of the EU Referendum act to its final royal assent in December 2015. The site includes links to the Bill, statements and discussion in parliament and revisions.
The Electoral Commission website has details of debate about the wording of the question. Its website also has a media briefing and background information on the timing.
This followed a number of years of discussion about the process. The Guardian has a transcript of David Cameron's speech from 2013 which outlined plans.
It was also a pledge in the 2015 Conservative Party manifesto.
The official campaign group website include: Britain Stronger in Europe Britain Stronger in Europe (formally The In Campaign Ltd) is a lobbying group campaigning for the United Kingdom to remain in the European Union key members Danny Alexander, Peter Mandelson
Leave.EU- The campaign was co-founded by Bristol-based businessman and UKIP donor Arron Banks, with property entrepreneur Richard Tice.
Grassroots out cross party group include Kate Hoey, Peter Bone
Conservatives for Britain - Supporters Lord Lawson campaigning for a new relationship with EU.