World Book Day was established by Unesco as a way of encouraging reading for leisure.
First celebrated in 1995, the annual event falls on April 23 each year.
While some may mark the occasion by choosing to return to old favourites, it may also be a good time to pick up a new novel that has won over readers past and present. This list below features some of the most popular works of all time.
However, a lack of comprehensive sales figures for several popular titles, including Alexander Dumas's The Count of Monte Cristo, Miguel de Cervantes's Don Quixote and J R R Tolkien's The Lord of the Rings – which has been sold as a trilogy as well as a single issue – makes it difficult to come up with a definitive list.
But, based on our research, here are 10 of the best-selling books of all time.
1. ‘Don Quixote’
The classic by Miguel de Cervantes crowns the list, which seems fitting as the date for World Book Day was selected to mark the day of his death.
Published in 1605, Don Quixote may have an unfair advantage over some of the other entries in this list, as the work is considered to be the first modern novel. It has sold more than 500 million copies to date.
2. ‘A Tale of Two Cities'
Published in 1859, the historical novel by Charles Dickens takes place in London and Paris before and after the French Revolution. The novel has an unshakeable grip on popular culture and has had several film, television, radio and theatre adaptations. It has sold more than 200 million copies.
3. ‘The Lord of the Rings’
When it was published in 1954, J R R Tolkien's The Lord of the Rings trilogy opened up a doorway to a whole new world. Inhabited by orcs, elves, dwarfs and hobbits, each with their own culture, language and way of life, Tolkien's Middle-earth felt startlingly real and is one of the most detailed novels in existence. The work has sold more than 150 million copies.
4. ‘The Little Prince’
With its bright illustrations and crisp sentences, it is easy to dismiss Antoine de Saint-Exupery's The Little Prince as a children's book at first glance. But the cosmic, cross-universe magic of the novel confronts the jaded nature of adulthood. With fantastical characters including the Little Prince himself, a king with no subjects, a businessman who catalogues the stars aiming to own them all, a talking fox and a rose, the novel takes the reader on an adventure of love and loss. The Little Prince has sold more than 140 million copies.
5. ‘Harry Potter and the Philosopher’s Stone’
The book that started a modern cultural phenomenon and turned its author into one of the richest women in the world. Harry Potter and the Philosopher's Stone has sold more than 120 million copies since it was first published in 1997. Being translated into 80 languages no doubt helped. If you're wondering, Harry Potter is the best-selling book series in history, having collectively sold more than 500 million copies.
6. ‘The Hobbit’
A prequel to The Lord of the Rings, Tolkien's The Hobbit was published in 1937. The book gained admiration for helping hone the literacy skills of young readers. The work is often hailed as one of the best fantasy works ever written and has sold more than 100 million copies.
7. ‘And Then There Were None’
Agatha Christie's And Then There Were None is the world's best-selling mystery. There have been numerous adaptations of the novel in film, radio, television and theatre. The novel was also the inspiration for a 1980 video game called Mystery House as well as a 2005 game that retained the book's name. And Then There Were None has sold more than 100 million copies.
8. ‘Dream of the Red Chamber’
Also called The Story of the Stone, Cao Xueqin's 18th-century work is considered to be a zenith in Chinese literature. The work is believed to be based on Xueqin's own life, as well as the rise and fall of his family. Dream of the Red Chamber is praised for its accurate description of social structures and life in 18th-century China, ruled by the Qing dynasty. It has sold more than 100 million copies.
9. ‘The Lion, the Witch and the Wardrobe’
Written by C S Lewis, The Lion, the Witch and the Wardrobe offers as much to adult readers as to its young target audience. Telling the story of four siblings who walk through an old wardrobe into another world, the story is replete with breathtaking imagery. The work has sold more than 100 million copies since its publication in 1950.
10. ‘The Da Vinci Code’
Dan Brown’s thriller was a worldwide sensation when it was published in 2003 and made symbologists out of us all. The novel puts forward an alternative religious history and sparked interest in the legend of the Holy Grail and the role of Mary Magdalene in Jesus's life. The novel has been translated into 44 languages and has sold more than 80 million copies.