That the reliability of articles and statistics found on Wikipedia are a bit questionable will be our starting point, the "given" of this little exercise. That said, I think some interesting "truths" can be gleaned from the site's list of all-time bestselling books.
Do keep in mind that the list makes a distinction between "most published and distributed" and "best selling." That eliminates contenders like the Bible, the Qur'an, and Quotations from Chairman Mao. Too, sales figures for individual Harry Potter and Twilight books are, for some reason, said to be so unreliable that they are not included in the list (although the Potter series is estimated to have sold more than 450 million copies in total, and the Twilight series, some 116 million copies).
If we accept these standards, the best selling single-volume books of all-time are said to be:
- A Tale of Two Cities - Charles Dickens - 1859 - 200 million copies +
- Le Petit Prince - Antoine de Saint-Exupery - 1943 - 200 million
- The Lord of the Rings - J. R. R. Tolkien - 1954-1955 - 150 million
- The Hobbit - J. R. R. Tolkien - 1937 - 100 million
- Dream of the Red Chamber - Cao Xuequin - 1754 - 100 million
- And Then There Were None - Agatha Christie - 1939 - 100 million
- The Lion, the Witch, and the Wardrobe - C. S. Lewis - 1950 - 85 million
- She - H. Rider Haggard - 1887 - 83 million
- The Da Vinci Code - Dan Brown - 2003 - 80 million
- Think and Grow Rich - Napoleon Hill - 1937 - 70 million
- The Catcher in the Rye - J. D. Salinger - 1951 - 65 million
- The Alchemist - Paulo Coelho - 1988 - 65 million
- Steps to Christ - Ellen G. White - 1892 - 60 million
- Lolita - Vladimir Nabokov - 1955 - 60 million
- Heidi's Years of Wandering and Learning - Johanna Spyri - 1955 - 50 million
- The Common Sense Book of Baby and Child Care - Dr. Benjamin Spock - 50 million
- Anne of Green Gables - Lucy Maude Montgomery - 1908 - 50 million
- Black Beauty: The Autobiography of a Horse - Anna Sewell - 50 million
- The Name of the Rose - Umberto Eco - 1980 - 50 million
- The Eagle Has Landed - Jack Higgins - 1975 - 50 million
- Watership Down - Richard Adams - 1973 - 50 million
- The Hite Report - Shere Hite - 1976 - 48 million
- Charlotte's Web - E. B. White - 1952 - 45 million
- The Ginger Man - J. P. Donleavy - 1955 - 45 million
- The Tale of Peter Rabbit - Beatrix Potter - 1902 - 45 million
A few things immediately jump out at me:
- Being originally published in the English language is a huge advantage (as 20 of the top 25 were),
- But one book each in French, German, Portuguese, Italian, and Chinese cracked the top 25,
- Children and YA books are quite well represented,
- Quality is not required for a book to become a massive bestseller (as in, The Da Vinci Code and She),
- Dr. Spock and Shere Hite made the list with "medical" books,
- The only religious book to make the list was published way back in 1892, and
- I doubt that some of these books are being much read at all these days.
Interestingly, just out of the top 25 are books like: Jonathan Livingston Seagull, Angels and Demons, and Valley of the Dolls (God, help us, I kid you not on these three) and War and Peace and To Kill a Mockingbird.
As you can see from the ballpark-sized rounding off of these numbers, lots of books are grouped together and are really impossible to rank. But I do suspect that the rankings shown are relatively correct.