EFL League One
The English Football League One (often referred to as League One for short or Sky Bet League One for sponsorship reasons, and known as the Football League One from 2004 until 2016) is the second-highest division of the English Football League and the third tier overall in the entire English football league system.
League One was introduced for the 2004–05 season. It was previously known briefly as the Football League Second Division and for much longer, before the advent of the Premier League, as the Football League Third Division.
At present, Gillingham hold the longest tenure in League One, last being out of the division in the 2012–13 season. There are currently seven former Premier League clubs competing in League One, namely Sheffield Wednesday (1992–2000), Ipswich Town (1992–95 and 2000–02), Charlton Athletic (1998–99 and 2000–07), Bolton Wanderers (1995–96, 1997–98 and 2001–12), Portsmouth (2003–10), Wigan Athletic (2005–13) and Sunderland (1996–97, 1999–2003, 2005–06 and 2007–17).
Wikipedia — https://en.wikipedia.org/wiki/EFL_League_One