Middlesbrough have signed Huddersfield midfielder Adam Clayton for an undisclosed fee with Jacob Butterfield going in the opposite direction.
Clayton, 25, who had been expected to join Boro last week, made 85 league appearances in two seasons with the Terriers after joining from Leeds.
Butterfield, 24, joined the Teessiders from Norwich last September and made 32 appearances in all competitions.
Both players have signed four-year deals with their new clubs.
Former Manchester City trainee Clayton could make his Boro debut at Leeds on Saturday, while Butterfield is likely to make his Town bow at Cardiff later the same day.
Middlesbrough boss Aitor Karanka told the club website: "Adam is another player who will improve our squad and I'm delighted to welcome him to Boro.
"He is a strong player and a strong character and just the sort of person I want in my squad."
Meanwhile, the Terriers have also added 17-year-old Airdrieonians striker Liam Coogans for an undisclosed fee.
The teenager, who has already made 33 first-team appearances, scoring four goals, will initially join up with the club's academy side.
Huddersfield caretaker manager Mark Lillis said: "It's testament to his talent that he has already played so much senior football at his age, but he will now take on a new challenge as he makes the step from part-time to full-time football in our academy."
Airdrie manager Gary bollan predicted that Coogans would "go far in the game".
The Diamonds' chairman, Jim Ballantyne, added: "Liam has worked hard and has had a fairly dramatic entry to first-team football. His debut was in a season that was very difficult for the Club and he coped really well."