WAKO
The largest amateur governing body, running five distinct competitive disciplines rather than one.
WAKO — the World Association of Kickboxing Organizations — is the main amateur body and the route by which most European competitors enter the sport. Its significance for anyone studying rulesets is that it does not run one discipline but five: point-fighting, light-contact, full-contact, low-kick and K-1 rules.
Those are genuinely different sports rather than difficulty tiers. A national champion in point-fighting, contested on a tatami with the bout stopped after every scoring technique, is doing something almost unrelated to a national champion in K-1 rules, contested in a ring with knees and a brief clinch. Crossover between them is poor in both directions.
The K-1 category is the newest and fastest-growing precisely because it is the one that prepares a fighter for the ruleset they will actually meet if they turn professional.