Motherwell land Irish under-21 international midfielder Ross Tierney
The 20-year-old attacking midfielder has signed a three-and-a-half-year deal from Bohemians for an undisclosed fee.
"He is a young player who has had a couple of excellent seasons with Bohemians and his national squad.
"His attributes will fit in perfectly with how we play and his potential is unlimited at this stage of his career.
"He's already met the squad and is excited about the move. We mirror those feelings."
Tierney, will join when the transfer window opens and has made 67 appearances for Bohemians. He was recently nominated for PFA Ireland's Young Player of the Year and included in Ireland's Under-21s squad where he headed the winner against Australia on his debut in June, the first of his five caps to date.
Meanwhile Aberdeen have secured the future of young winger Ryan Duncan until 2024 after agreeing a two-year extension to his existing deal at Pittodrie.
The 17-year-old is currently on a half-season loan in League Two at Peterhead for senior level experience but has also hit double figures in the under-18 league this season.
“I now have two, three years to try and push myself into the team and try to become a regular,” he said. “It is the perfect place for me to develop my game and hopefully I can make it through to the first team as soon as possible.”