The Legend of Korra has 4 seasons, which the series calls Books.
The four Books are Book One: Air, Book Two: Spirits, Book Three: Change, and Book Four: Balance. Together they form the complete animated series, which contains 52 episodes. Each Book presents a distinct major conflict while continuing Korra’s development as the Avatar.
The terminology can cause confusion because “Book” does not mean a separate publication or a partial season in the usual sense. In The Legend of Korra, it is the show’s title for a season-length story arc. Book One was initially conceived as a 12-episode miniseries, but Nickelodeon later ordered enough additional episodes to create four Books.
Book Four: Balance is the final season. It aired in 2014 and takes place three years after the events of Book Three. Unlike the original Avatar series, which had three Books, Korra’s story was structured around four, making 4 the correct total.