Brentford, Chelsea, Exeter City left after last years competition, while Bolton Wanderers, Crewe Alexandra, Doncaster Rovers, Gillingham, Leeds United, Millwall, Peterborough United, Plymouth Argyle, Preston North End, Queens Park Rangers, and Sheffield Wednesday did not return after 3 years in the competition.
Two qualifying rounds were required to finalise the 32 teams that would enter the Group Stage.
In the Second Qualifying Round, the three winners were joined by Barnsley and Watford (the two teams who finished bottom of their respective Category 2 leagues in 2015/16).
Of the five teams in the Second Qualifying Round draw, one received a bye straight to the Group Stage, with the two winners joining them.
Note: Flags indicate national team as defined under FIFA eligibility rules; some limited exceptions apply.