Scottish Rugby's home is to be renamed the BT Murrayfield Stadium in a multimillion-pound sponsorship deal.
The communications giant also becomes sponsor of Scottish Rugby's four new academies for young people who aspire to play professionally.
Under the four-year partnership, BT also becomes sponsor of the Scotland 7s side from the outset of the 2014-15 HSBC Sevens World Series, and of Scotland's domestic league and cup competitions from next season.
Scottish Rugby Union chief executive Mark Dodson said it was a "momentous day" for the sport.
He said: "We are very proud to bring BT back into our family of sponsors on a size and scale that is unprecedented both for Scottish Rugby and, we believe, Scottish sport.
"While the headlines may be dominated by the naming rights of the stadium, today's announcement underlines BT's alignment to our own values and goals, particularly that rugby clubs are the heart and soul
of their communities that offer a welcome to all, young and old, boys and girls, men and women.
"This new funding underlines our desire to deliver more opportunities for young people to take up our game and broaden the reach of rugby across Scotland.
BT Sport sponsors both Glasgow Warriors and Edinburgh Rugby.
Dominic McKay, Scottish Rugby director of commercial operations, communications and public affairs, said: "We are delighted to have secured such a renowned and respected global partner. BT recognises the importance and the rich heritage associated with Murrayfield and Scottish Rugby.
"In branding our home the BT Murrayfield stadium, it reiterates our joint view that the name of the home of Scottish rugby that has been synonymous with the game in our country since 1925 had to be retained."
He added: "To secure a deal of this nature for the first time in our history means a huge amount for Scottish Rugby, as it will deliver very positively for us for years to come to enable us to continue to invest
in our game throughout Scotland."
John Petter, chief executive of BT Consumer, said: "We're delighted to be announcing this partnership today, furthering the relationship between BT Sport and Scottish Rugby's pro-clubs, to support and grow the game in Scotland."