The 26-year-old opted not to sign a new deal with Rangers and has agreed a two-year contract at the Riverside.
Boro boss Neil Warnock has said he wants to bring in eight or nine new signings for next season, while the squad was clearly light in the goalkeeper department.
Here’s how some fans reacted to the news online.
@ThomasPeacock_: Happy with that. Nothing spectacular but just need a solid keeper so we can focus on other areas
@tom_mcgarry17: No messing about and a shrewd addition, welcome Joe!
@TeessideCommie1: A good bit of business. A solid keeper with Championship experience. I'm personally happy with this.
@JoeHarston: No messing about love to see it. Begging this is the end of our keeper woes since Randolph left us
@ClarkRDanny: Bargain this for a free transfer!
@Smithy_MFC84: Hopefully a sign of things to come - identify the areas that need major reinforcements and move swiftly to bring them in.
@georgej24025969: Was quality when he came on for QPR at the Riverside so hopefully he does a job for us
@Kitney03: Had a class game against us earlier on in the season. First one down hopefully more to come
@GrahamS05892904: One down eight to go, good start hope Joe has a long career with the Boro
@ScottBlair19: After what I witnessed last season watching Bettinelli I’d take anyone!