First Team duo Martin Cranie and Tomas Mejias are among those to depart as the club confirms its retained list for the 2018/19 season.
Having joined from Huddersfield Town in January, defender Cranie leaves the club at the end of his short-term contract.
It is the end of a four-and-a-half year stay on Teesside for goalkeeper Mejias, who arrived from Real Madrid in 2014.
Meanwhile, Lewis Baker, Mo Besic and Jack Harrison head back to their parent clubs, Chelsea, Everton and Manchester City respectively, at the end of their loan deals.
Antonio Barragan, Martin Braithwaite, Julien De Sart and Ashley Fletcher return to Boro after spells out on loan.
A number of Academy players will also leave Boro this summer.
First Team players released at end of contracts:
Under-23s not offered new contracts:
Academy Scholars not offered new professional contracts:
Middlesbrough Football Club would like to take this opportunity to thank all departing players for their contribution throughout their time at the club.