Motherwell captain Peter Hartley is among 10 players leaving the club.
Goalkeepers Mark Gillespie and Rohan Ferguson, defender Richard Tait, midfielder Christian Ilic, Adam Livingstone and forward Christy Manzinga are also leaving Fir Park.
Rolando Aarons, Mikael Ndjoli and Mark O'Hara return to Newcastle United, AFC Bournemouth and Peterborough United, respectively after loan spells.
Well boss Stephen Robinson thanked all the players for their contributions.
"They leave us with our best wishes for the future," he added.
Striker Tony Watt has signed a new one-year deal with the Scottish Premiership club.
Charles Dunne, Christopher Long, Barry Maguire, Peter Morrison, Harry Robinson and Yusuf Hussain have all been offered extended deals, Motherwell said.