LINCOLN, Neb. - So long, Big Twelve. Nebraska's membership in the Big Ten Conference is official.

The Big Ten's board of presidents and chancellors unanimously welcomed Nebraska to the club on Friday, just a few hours after the school formally disclosed its interest. It takes effect July 1, 2011.

Also Friday, Boise State accepted an invitation to join the Mountain West Conference, as the two-time Fiesta Bowl winner seeks out a league that is a better launching pad into lucrative bowl games.

Boise State, now with the Western Athletic Conference, would become the Mountain West Conference's 10th member. The move would be effective July 1, 2011.

Nebraska chancellor Harvey Perlman said his school's move offers stability "that the Big Twelve simply cannot offer."

Nebraska is the Big Ten's first addition since 1990, when Penn State joined, and it comes just six months after the league announced that it was looking at expansion.

The move is a potentially crippling blow to the Big Twelve and the biggest move yet in an off-season overhaul that will leave college sports looking much different by this time next year.

"We've had a couple of disappointing days with the departure of two valued members," Big Twelve commissioner Dan Beebe said during a teleconference.

Beebe vowed to work to keep the 10 remaining members together but acknowledged that other Big Twelve schools are mulling their options.

Perlman said he believed Nebraska is much more "aligned" with the Big Ten than the Big Twelve when it comes to academics, culture, and athletics.

The university issued a statement that said for more than 20 years, Nebraska has compared itself to a list of 10 peer institutions established by the regents. Five of the 10 are Big Ten members; four are former Big Eight schools that joined Nebraska in the Big Twelve in 1996.

"The University of Nebraska would have new opportunities with membership in the Big Ten - and I believe the Big Ten would be a stronger conference as well," university president J.B. Milliken said.

Nebraska's move comes at the end of a crazy week in college athletics.

On Thursday, fellow Big Twelve member Colorado announced it was leaving for the Pacific Ten Conference. Texas and other schools in the Big Twelve South - Perlman told the regents that the Pac-10 had been in touch with many schools in that division - could be the next to leave. Texas regents scheduled a meeting for Tuesday to discuss the Longhorns' Big Twelve future.

"One school leaving a conference does not destroy a conference," Perlman said. "Nebraska did not start this discussion. After the Big Ten announced it planned to consider expansion, we saw reports that Missouri would want to go to the Big Ten, including a statement by their governor, a member of the board of curators, and chancellor - comments that weren't clearly supportive of the Big 12."

Nebraska athletic director Tom Osborne, the longtime football coach, agreed.

"As we read the tea leaves and listened to the conversations, some of the schools that were urging us to stay, we found some of them had talked to not only one other conference or two but even three, and those were the same ones urging us to stay," he said.

To generations of Nebraska fans, going to the Big Ten at one time would have been unthinkable. The school's athletic tradition is built on more than a century of football games against the likes of Missouri and Kansas, dating from the days the team was known as the Bugeaters.

The Huskers, in fact, have been conference partners with Iowa State, Missouri, Kansas, Oklahoma, and Kansas State since 1928; with Colorado since 1948 and with Oklahoma State since 1960.

Now the Huskers are on the verge of taking their five national titles in football, three Heisman Trophies, and enthusiastic fans east. They will look to start building new traditions, such as a border rivalry with the Iowa Hawkeyes and regular trips to Ohio State, Michigan, and Penn State.

Watching a football camp at Beaver Stadium, Penn State coach Joe Paterno declined to comment Friday. Paterno in the past has advocated for enlarging the Big Ten from 11 schools to 14.

"It's just the tip of the iceberg right now," Penn State receivers coach Mike McQueary said of Nebraska. "Unbelievable tradition, the things they've done in that program; academically as well."