In addition to individual ebooks, Yesterdays Classics offers our high quality ebooks for purchase in two kinds of collections: treasuries and sets. A Yesterday's Classics ebook treasury consists of all the ebooks published by Yesterday's Classics within a specific time period, with each treasury including dozens of books from many genres for children of a range of ages. Treasuries are ideal for families with children of different ages and interests, or for a young reader to work through as their reading abilities and interests mature. Ebook sets, on the other hand, are smaller groups of related ebooks, focused on a particular theme or author.