List of best-selling books Between 50 million and 100 million copies Between 50 million and 100 million copies

| Book_series | Author | Original_language | No_of_installments | First_published | Approximate_sales |
|---|---|---|---|---|---|
| The Hardy Boys | various authors as Franklin W. Dixon | English | 190 | 1927–present | 50 million |
| The Bobbsey Twins | various authors as Laura Lee Hope | English | 72 | 1904–1979 | 50 million |
| Tarzan | Edgar Rice Burroughs | English | 26 | 1914–1995 | 50 million |