2017–18 Isthmian League
The 2017–18 season was the 103rd season of the Isthmian League, which is an English football competition featuring semi-professional and amateur clubs from London, East and South East England. It was also the twelfth season for the current incarnations of the Premier, North and South Divisions, the last to have two regional divisions, and the first as the Bostik League following a sponsorship deal with Bostik.
In May 2017, the FA chose the Southern League to create one additional division at Step 3 and the Isthmian League to create one at Step 4 as part of the next change to the structure, and in March 2018, the Northern Premier League voted to reorganise its Step 4 divisions into an east-west alignment, with all Step 3 divisions contracting to 22 clubs and those at Step 4 to 20, taking effect in the 2018–19 season.