Martin Schulz is President of the European Parliament
David Cameron needs to choose "compromise over confrontation" when negotiating on future UK membership of the EU.
The EU has always functioned on the basis of compromise. The very culture and raison d'être of the EU are eminently ones of compromise.
This style works because no single country can become isolated. This is important in a system where one country saying 'no' is enough to block an outcome. Under these circumstances, a willingness to compromise is vital. Better results will emerge from working with, and not against, the cultural mind-set of EU decision-making.
This needs to be a debate about every member state, not just Britain. That way all governments can look at the outcome and see that the EU has been strengthened and is better equipped to face its challenges.
The EU and Britain have more in common than we have disagreements, and we should build on that positive aspect. I hope Mr. Cameron will accept my invitation to address the European parliament on his reform proposals.
Manfred Weber (DE) is chair of Parliament's European People's Party group
We in the EPP want the UK to remain part of this community, and we think – and hope – that the British people will confirm this. We believe that both the EU and the UK will be stronger together.
It is up to David Cameron to outline his vision for the future of the UK in Europe, but his contribution will be a part of a wider cathartic process. We will all benefit from constructive discussions on making the EU more efficient.
The UK’s opt-outs should be part of this discussion. Where it does have an opt-out, it should no longer have the right of veto, nor should it participate in votes by qualified majority. This is fair. The UK may not wish further integration, but that should not allow it to hold back those member states that do.
Knut Fleckenstein (DE) is a vice-chair of Parliament's Progressive Alliance of Socialists and Democrats group
I don’t like to think of the EU without the UK. However, a referendum will bring clarity on their future role, be inside as members or outside as neighbours.
However, as much as I and many others want the UK to remain, it does not mean we should offer any special deals. Fundamentals like Schengen should not be up for discussion. These are cornerstones of the EU and are too high a price to pay.
We need to wait and see the outcome of the referendum. Although I am optimistic, I think we should also play our part, and show the UK that EU membership is mutually beneficial.
Syed Kamall (UK) is chair of Parliament's European Conservatives and Reformists group
The referendum will clarify the relationship between the UK and the EU, which has to be a good thing. People I talk to in Brussels have different expectations for the EU than those of my constituents in London.
It appears that the majority of people in Britain favour a common market and cooperation, but not an ever-closer political union. If they can achieve that, they are more likely to vote yes to continuing membership. They are also less likely to present a barrier to those member states that do seek closer integration.
On the other hand, if they feel shackled to a project with a United States of Europe as its end goal, then freedom for the UK to negotiate its own agreements with the rest of the world becomes ever more appealing.
Pavel Telička (CZ) is a vice-chair of Parliament's Alliance of Liberals and Democrats for Europe group
The forthcoming UK referendum is an opportunity to have a much needed-discussion on the evolution of the EU. Come the event, I believe that the British will see that on balance, ‘Brexit’ would be a bad deal for Britain.
However, if it stimulates discussions on EU reforms, then that will be a good thing. If it leads to treaty change, then let’s use that to ensure that there are no more rebates, no more opt-outs. In future, everyone will play by the same rules.
Gabi Zimmer (DE) is chair of Parliament's European United Left/Nordic Green Left group
I don’t wish to see an EU without the UK, nor do I wish to see a 'two speed' EU. What I do want is an EU that protects social and democratic rights. I think the UK Prime Minister is taking a major risk in trying to pacify the far-right anti-EU and anti-immigration forces conceding to their demands.
Right-wing populists in France, Hungary, Germany and Scandinavia are growing in popularity because people feel that the EU is in deep political crisis. They are correct; in its current shape, the EU is failing to protect people's social interests.
I always advocate democratic decisions, and I want everyone in the EU to vote for a new treaty that places social protection, parliamentary decisions and democratic participation first.
Rebecca Harms (DE) is co-chair of Parliament's Greens/European Free Alliance group
The EU is nothing without a unity of purpose among all its members, and if a major member state chooses to leave, that would be a serious blow. Yet the British political establishment has managed to sleepwalk its way into a referendum on a potential 'Brexit'.
It is incumbent on all political actors; within Britain and across Europe, to support and argue the case for Britain to remain a member. However, the one positive is that irrespective of the referendum outcome, it will bring closure to the debate.
Nigel Farage (UK) is co-chair of Parliament's Europe of Freedom and Direct Democracy group
I am thrilled at the prospect of a referendum. It is the only way to properly settle this issue. I want this debate to be open, free and fair, with the British people deciding this issue for themselves. We don’t need power-hungry bureaucrats in Brussels interfering by funnelling huge sums into media outlets in a bid to buy the result.
I am glad to hear that the term 'Brexit' has been accepted into the Oxford English Dictionary (OED). It shows that even linguistically we are gaining both traction and legitimacy. As an ominous harbinger of things to come, the OED also contains the word 'Grexit'. Europhiles should beware.