This is Jeremy Corbyn's first big electoral test, writes Phil Hornby.
One year after the general election, with the Conservatives split from top to bottom over the EU, you'd expect Labour to pick up lots of seats.
His problem is that the council seats up for election were last contested in 2012, when Labour did very well. So, to make gains, Mr Corbyn has to do even better than that.
The opinion polls suggest that will be a very tall order. He remains very popular among his party members and very unpopular among his MPs. Tonight we'll find out how popular he is with voters.
Winning Southampton was Labour's crowning glory in 2012. It looks vulnerable tonight. So does Crawley, where the Tories need to make just one gain to take control. Labour's hold on Hastings,Reading and Oxford looks firmer. When all the results are in, it could be that Hastings is Labour's only council south of the M4.
The Conservatives have high hopes of taking overall control of a handful of councils including Maidstone, Hart, Portsmouth, Southend and Basildon.
The Lib Dems have got to make gains if they're to begin to recover after last year's disastrous general election. They're looking to pick up seats across the region, and to maintain their dominance in Eastleigh.
The Greens hope to do well in Oxford. But what of UKIP? They've had a year of splits and infighting but are still doing reasonably well in the opinion polls. Nigel Farage is confident they'll make progress tonight.
There are Police and Crime Commissioner elections everywhere. Last time, they took place in November, turnout was extremely low and Independents won in Kent, Hampshire & the Isle of Wight, Surrey and Dorset. The main parties will be hoping they can take advantage of a higher turnout: the Independents will find it tougher this time.
For once, politicians have only half an eye on these election results. Their main concern is the next time we go to the polls, in seven weeks' time. The EU Referendum result will, of course, reverberate long after these local elections have been forgotten.