It's the most eagerly anticipated vote for years - but there seems no doubt who'll win, writes Political Correspondent Phil Hornby
The government will get parliament's permission to trigger Article 50. Brexit will then become a reality - although the government are keen to stress the point of no return was last June.
The vast majority of MPs in our region, including all the Tories who backed Remain, are going to support the Government. They say the result of the referendum must be respected. Brighton Pavilion MP Caroline Lucas, co-leader of the Greens, will vote against.
So will her neighbour Labour MP Peter Kyle from Hove. He will defy Jeremy Corbyn's instructions. He says he accepts the UK is leaving the EU, but says more time is needed to get a proper plan for Brexit in place before Mrs May pulls the trigger.
Oxford East Labour MP Andrew Smith will follow his party line. Most of his voters supported Remain. But he says he will vote to trigger Article 50 because the overall referendum result was clear.
He says he will support amendments to retain strong links with the Single Market (there are 80 amendments which could be debated) but when it comes to the main vote he'll support the Government. When he told a public meeting in Oxford last week what he was planning to do, one person told him he'd have trouble getting re-elected.
So the Government will win the big vote tomorrow, and the bill will almost certainly get through the Lords later this month.
Mrs May should be in a position to trigger Article 50 in the second week of March.
Then the hard work really starts.