Three downs, a field that's 10 yards wider and longer, with end zones 10 yards deeper. Evolved from Canadian rugby, with sides of 15 reduced to the current 12 early in the 20th century - the first attempt to Americanize the game. A later Americanization came in the 50s, and was the start of a 20-year period in which leagues on both sides of the border competed to sign top US talent. As the NFL and AFL boomed, thanks to the infusion of Big TV money that began in the 60s, the parity was lost.

In addition to the differences mentioned by pingouin:

• The rouge or single is a one-point score (for the kicking team) for any kick that the kicking team downs in its end zone. Therefore, even missed field goal attempts can score one, as...
• the uprights are on the goal line, similar to American football of the 1960's and earlier. The practical upshot of this is that all kicks are returned, including missed FGs.
• motion prior to the snap is legal for all offensive players not on the line or at quarterback

The Canadian Football League expanded into the U.S. in the mid-1990s, had a television contract with ESPN2, and for a time was close to solidifying this new expansion base by renaming the league the Continental Football League. As U.S.-based teams started folding, this idea was abandoned. As of 1996, the CFL returned to being a solely Canada-based league.