Isthmian League 2018–19

The 2018–19 season will be the 104th season of the Isthmian League, which is an English football competition featuring semi-professional and amateur clubs from London, East and South East England. Also, it is the twelve season for the current incarnations of the Division One North and Division One South.

To Premier Division
Promoted from Division One North

Promoted from Division One South

Relegated from National League South

From Premier Division
Promoted to National League South

Relegated to Division One North

To Division One North
Promoted from Eastern Counties League

Promoted from Essex Senior League

Promoted from Spartan South Midlands League

Relegated from Premier Division

Transferred from Southern League Division One Central

From Division One North
Promoted to Premier Division

Relegated to Eastern Counties League

Relegated to Essex Senior League

Transferred to Division One South

To Division One South
Promoted from Southern Combination League

Promoted from Southern Counties East League

Transferred from Division One North

From Division One South
Promoted to Premier Division

Relegated to Combined Counties League

Relegated to Southern Combination League

Relegated to Southern Counties East League