There were 30 volumes, written between 1899 and 1926. Mr. Bobbsey is a prosperous lumber merchant. Mrs. Bobbsey is a housewife. Bert and Nan are the older twins, and Flossie and Freddie are the younger set. Later in the series he re-emerges as a major character, an even worse bully, and for a large portion of the series is the Bobbseys' nemesis in every book.
Some important items appear in one book, never to be seen again.
In The Bobbsey Twins on Blueberry Island the twins have a goat andgoat cart. It never appears again. In The Bobbsey Twins in the Great West the plot hinges around Mrs. Bobbsey's inheritance of both a lumber tract and a ranch. They never appear again. On the other hand, some characters appear and seem to reappear and reappear, such as Aunt Sally Pry, who is a major player in some of the books in the late 1920s.