When Peggy Olson got crazy high on pot this week, that was surprising.

But Mad Men getting picked up for a fourth season by AMC? Not exactly a shocker.

“We always saw the potential for Mad Men,” said network president Charlie Collier. “It’s been extremely gratifying to see the show develop in to such a pop-cultural phenomenon with such a passionate fan base.”

The August 16 season three premiere drew a series-record 2.8 million viewers. Since then, viewership has remained steady.

It's unclear how long Mad Men will remain on the the air, but creator Matthew Weiner has said he'd like to complete the 1960s. If the show continues to jump ahead two years every season, that would guarantee at least six full seasons of this brilliant series.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.