While the partnership is for all sports, its most high-profile results will be seen in football and basketball.
The two 12-team leagues are aiming to create a 12-game inter-conference schedule by the 2017 season that would have each school play an opponent from the other conference every season.
Increased competition between the leagues in sports other than football could start as early as next year.
"From my perspective this improves the scheduling and creates more high-profile matchups," Pac-12 Commissioner Larry Scott said. "It gets us exposure into the Midwest and East Coast on the Big Ten media platforms, the Big Ten Network and ESPN. And we hope it brings some rivalries that are rooted in a 100-year tradition of the Rose Bowl.
The Big Ten and Pac-12 have been Rose Bowl partners for decades.
"For me it's a creative way to accomplish a lot of things the conferences seek through expansion without having to expand," Scott said.
Scott said the idea bloomed after the Pac-12 presidents rejected the idea of further expansion back in October.
Scott's league added Utah and Colorado this year to increase to 12 members and the Big Ten added Nebraska as its 12th member. Both leagues played conference championship games in football for the first time earlier this month.
Big Ten Commissioner Jim Delany said his league came to the conclusion that getting bigger wasn't getting better.
"When we looked at models for 14 or 16 teams we couldn't see how we weren't diluted," Delany said. "But we continued to look at ways to make ourselves more interesting, increase our reach, make ourselves more national."
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