The Arizona Cardinals shared Palmer's open letter announcing his retirement in which he said he will "never forget" the relationships he developed and will "especially miss the grind" that came with playing football at the highest level for so long:
Palmer entered the league in 2003 when the Cincinnati Bengals drafted him with the No. 1 overall pick out of USC. He looked like a franchise quarterback in the Queen City at times, throwing for more than 3,000 yards in five different seasons and leading the team to the playoffs twice.
However, he asked for a trade before the 2011 campaign and briefly retired until the Bengals granted his wish. Cincinnati shipped him in October 2011 to the Oakland Raiders, for whom he played until they dealt him to the Cardinals in April 2013.
He was a Cardinal ever since and helped lead the team to the playoffs in the 2014 and 2015 seasons, though he missed the 2014 playoffs because of injury.
Palmer never won a Super Bowl, but he was a three-time Pro Bowler who threw for 46,247 yards and 294 touchdowns with 187 interceptions. He finished with six seasons of more than 4,000 passing yards and was one of the better quarterbacks in the league when he was healthy and playing at his best.
The idea of retirement is nothing new for Palmer, as Kyle Odegard of the Cardinals website noted in June that Palmer thought about hanging up his cleats during his 12th, 13th and 14th years in the league.
In February, Palmer had said he would "take some time after the  season to get away and see where I was physically and mentally," per Darren Urban of the team site.
After flirting with the notion a number of times, Palmer took the step at 38 years old.