The EU referendum campaign has officially begun - 10 weeks before Britain decides whether to leave the union.
Political heavyweights from Britain Stronger in Europe and Vote Leave will use rallies across the UK to try and persuade voters of their opposing cases.
Here's everything you need to know.
Boris spearheads 'Brexit blitz'
Boris Johnson will kick off a "Brexit blitz" as the first day of the official EU referendum campaign gets underway.
The mayor of London will make a series of speeches across the UK as the Vote Leave campaign utilises a politician many observers see as their biggest asset in convincing Britons of the case for leaving the union.
The NHS will be placed at the centre of their campaign, with Mr Johnson and his allies claiming that a Brexit would give the health service a multi-billion pound boost.
Vote Leave claims the UK's £10.6 billion net contribution to Brussels could be diverted to hospital beds and alleviate what it called a "crisis in the NHS".
Prominent anti-EU campaigners, including Justice Secretary Michael Gove and Commons Leader Chris Grayling, will also step up the Brexit campaign.
Darling warns of 'economic disaster'
Alistair Darling will make the case for staying in the EU when he makes a speech in London.
Darling, who was Labour chancellor between 2007 and 2010, will argue that leaving the EU would be "economic disaster" and accuse Brexit campaigners of offering a "fantasy future" outside the 28-member bloc.
He will warn that "dark clouds are gathering on our horizon" and a vote to leave would threaten Britain's long-term economic recovery and signal that it is a "country in retreat".
"If we choose to leave we will survive, but we will send an unequivocal signal that we are a country in retreat. Leaving is not a cost-free, risk-free experiment," he will say in a speech in London.
First official day of campaign
The first official day of the campaign sees rules governing spending and other areas come into force ahead of the historic June 23 vote.
Any individual or organisation that spends more than £10,000 on campaigning activities must register with the Electoral Commission.
The spending limit for a registered campaigner is £700,000, for the designated lead campaigners it is £7 million, and for political parties it is a variable amount between £700,000 and £7 million, based on the particular party's share of the vote at the last general election.