Monday Night Football turns 45 today—notably on a Monday! And as the Jets and Colts warm up for tonight's kickoff, fans will know it's game time when they hear four distinct, descending notes. But it wasn't always that way. The biggest game of the week has been soundtracked by a handful of theme songs, starting back on September 21, 1970.

When Monday Night Football premiered on ABC, it was accompanied by the thoroughly groovy, Hammond organ-heavy “Score” by Charles Fox. The composer had previously written the theme for ABC’s Wide World of Sports, and he would later make a name for himself doing the theme songs for Happy Days and The Love Boat, as well as composing Roberta Flack’s Grammy-winning “Killing Me Softly with His Song.”

“No network had ever programmed a regular sporting event in the evening in prime time,” Fox wrote in his autobiography, and though no one could know what a juggernaut the show would become, he set about writing a funky soul-jazz tune. The song was released under the alias “Bob’s Band”—presumably because Fox was employed at the time by Bob Israel’s Score Productions, a music company specializing in theme songs and background music.

Fox retained its rights over that song, but the show moved on to a new opener after a few years. “Monday Night Football is still on the air, but my theme was replaced after seven years by someone named … Bob Israel,” Fox wrote of his former boss. Well, almost. First, there was a version simply called “ABC – Monday Night Football Theme” that aired from 1976 to 1981. Then in 1982, Israel’s Score Productions was brought in to update that song. The three composers of the 1976 piece unsuccessfully sued for copyright infringement.

Then, in 1989, Johnny Pearson’s “Heavy Action” rang in a new era of watching live sports from the comfort of your La-Z-Boy. Though the company had retained the rights to the song a decade previously, they used it primarily as background music and didn't make it an official theme until '89. The first four notes of the British composer’s opener became synonymous with American football, and the song is likely one of the most widely and easily recognized themes in television history.

Also in 1989, country star Hank Williams Jr. reworked his earlier hit "All My Rowdy Friends Are Coming Over Tonight" into a bar-room blues rocker that spoke of "turning on [his] TV for some pigskin fun." The song was a huge success and ran in various forms on the program for over 20 years. Williams enthusiastically growling "Are you ready for some football?" became as identifiable to the show as the opening notes of "Heavy Action."

An early, pre-season promo featuring Williams' song.

Unfortunately, in 2011, Monday Night Football (which in 2006 moved from ABC to ESPN) dropped Williams' theme after he made controversial statements about President Barack Obama on Fox News. The network reverted to featuring "Heavy Action" most prominently, and this year for the 45th anniversary, they reworked the theme yet again. The latest intro, which will run before each of this season's games, features archive videos and computer generated players to highlight some of the greatest plays and playmakers in the history of the broadcast.

Yeah, we're definitely ready for some football.