From Bulbapedia, the community-driven Pokémon encyclopedia.
A chapter is the Pokémon Adventures equivalent of the anime's seasons. They divide the manga into sections, which have a separate plot, though the characters and events from one chapter may be used in another, later chapter. Each chapter is named after a main series game, and the characters introduced in each chapter generally share those names.
Chapters are further broken down into volumes, which are then separated into rounds. There is no definitive number of rounds in each chapter.
Twelve chapters have been released, of which first eight have been fully translated into English and published by Chuang Yi. Some rounds of the HeartGold & SoulSilver chapter have been released but this is not yet complete.
VIZ Media has fully translated and published the first three chapters and is now, after a publishing break, translating the Ruby & Sapphire chapter. In addition, the company is currently translating the Diamond & Pearl and Platinum chapters as a second series, titled Pokémon Adventures: Diamond and Pearl/Platinum. The company has released some of the Black & White chapter as a third series, titled Pokémon Black and White (mini-volumes) and Pokémon Adventures: Black & White (tankōbon-sized volumes), and started releasing the HeartGold & SoulSilver chapter as a fourth series starting in August 2013 under the name Pokémon Adventures: HeartGold and SoulSilver (although in the chapters sort, HeartGold & SoulSilver chapter is before Black & White chapter).
List of chapters