Olivia Colman and David Tennant are back as DS Ellie Miller and DI Alec Hardy, this time investigating the rape of a woman in the fictional Dorset town.
She's played by former Coronation Street actress Julie Hesmondhalgh.
Jodie Whittaker and Andrew Buchan return to play Beth and Mark Latimer, along with Arthur Darvill as local vicar Paul Coates.
Other cast members include  Lenny Henry, Georgina Campbell, Sarah Parish, Charlie Higson and Mark Bazeley.
The first episode, shown on Monday night, drew 7.5 million viewers.
That fell slightly short of the first episode of series two, which launched in 2015 to 7.6 million.
The debut episode of the first series, shown in 2013, pulled in 6.8 million.
Here's what the TV critics had to say about the start of the new series.
Read the full reviews from the Daily Mail, The Independent, the Daily Express, the Telegraph, The Times (subscription required) and the Radio Times.
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Broadchurch is back for its third and final series - and has gone down well with TV critics.