From Bulbapedia, the community-driven Pokémon encyclopedia.
The Orange League (Japanese: オレンジリーグ Orange League) is the regional Pokémon League of the Orange Archipelago. It consists of the Gym Leaders of the Orange Crew. It has been established for over 300 years.
The Orange League is perhaps the least conventional of all the regional Pokémon Leagues, as it focuses less on Pokémon battling and more on how a Trainer interacts with his or her individual Pokémon in many different circumstances. Orange League Trainers are said to be tougher than those in the Indigo Pokémon League. However, meeting the requirements to enter Orange League competitions is a much simpler task: Trainers must earn only four Badges instead of the usual eight.
According to Tracey, young Pokémon Trainers from the Orange Islands typically begin their Pokémon journey on Tangelo Island and work their way around the archipelago, winning Badges along the way. The Trainers' final destination is Pummelo Island, where Orange League competitions are held. Competing in the Orange League is different from competing in other Pokémon Leagues. Trainers may freely challenge the top Gym Leader in the Orange Crew, called the Head Leader, at any time. Those who can defeat the Head Leader in a Full Battle take the title of Pokémon League Champion, as well as the coveted Winner's Trophy. A photo featuring the winning Trainer with the trophy on hand and all six Pokémon that have participated in the full battle will be kept in the Palace of Victory, together with the footprints of the Trainer and the Pokémon.
The Orange League is only featured in the anime and in the manga The Electric Tale of Pikachu, as the Orange Archipelago is not accessible in any of the games.