The Isthmian League is a football league in England that operates at the semi-professional level. Founded in 1905, it is one of the oldest leagues in the country and features clubs primarily from London and the surrounding areas. The league is divided into several divisions, with promotion and relegation systems in place to allow teams to move between levels based on their performance. The Isthmian League is part of the National League System, which organizes football competitions in England. It serves as a crucial step for clubs aspiring to reach higher levels, such as the National League and eventually the English Football League. The league is known for its competitive spirit and community involvement.