Ashes-winning opener Cameron Bancroft will spend the majority of the 2018 campaign as one of Somerset's overseas players.
The 25-year-old has opened for Australia alongside David Warner in all three Ashes Test so far, scoring an unbeaten 82 on his debut in Brisbane where their opening stand of 173 secured victory.
Bancroft also has experience of English summer conditions, having spent last season with Gloucestershire.
He played in 11 Specsavers County Championship Division Two games in 2017, scoring 685 runs at an average of just over 40 - his top score was an impressive unbeaten 206 against Kent in September.
Bancroft will be available for the start of the four-day season, the entire Royal London One-Day Cup and six more County Championship games which take place after the NatWest T20 Blast.
He said: "I'm really excited to be joining a county with so much potential. I've heard a lot of good things about Somerset from Justin Langer and it's clear that they are a team heading in the right direction.
"There's a long history of Australians doing well at Taunton, so hopefully I can add my name to that list."