The struggling, famished writer is a bit of a hackneyed stereotype but research shows it's a truism, nonetheless. British newspaper The Guardian recently released a rather daunting article stating that most full-time professional writers make a  paltry £600 a month - that's under $1000 U.S. dollars. But of course, the authors we know about - those who come to the public attention - have already become celebrities, selling millions of books and making millions in the process. From the talented aspiring writer struggling to make the distant ends meet, to the world-renowned author winning international awards and making serious bank: What differentiates the two? Is it even possible to pin down the seemingly intangible nature of what makes one wordsmith successful over another? In an attempt to answer this question, perhaps we ought to look at certain celebrated writers - J.K. Rowling, E.L. James, and John Grisham, for example - and query what they have in common?

The answer is not immediately obvious. They all come from widely varying backgrounds, their novels are incomparable, and their styles disparate. However, each of these writers have one area of common ground; their successful novels are specifically 'genre' works. These authors are know, respectively, for fantasy, romance and mystery - and if the statistics show us anything it's that genre books sell better than your average literary piece, short story collection or poetry. Literary novels, those which can ill be pinned into one genre, tend to attract a niche audience, the sort of people who label themselves 'readers', perhaps frequenting vintage bookstores and grand libraries in their spare time. Genre readers, however, might be more likely to browse through their Kindle and purchase the latest novelty at the click of a button. This is, of course, a generalisation and not true of all genre or literary readers; but the fact is, genre readers have a voracious appetite and it's genre novels which are driving the publishing industry today.

The question of whether writers should limit themselves to a genre if they want to make a living depends, of course, on passion and investment. A writer, involved in the work for love over money, will write about what interests them. Sometimes, this will fit neatly into a popular genre. Genre writing, though, is notorious for having a rather formulaic checklist of things that need to be incorporated into the novels. Fantasy, for example, will need some form of magic, good and evil at war, and usually a hero or heroine. If you're a budding writer or a curious reader, and you're considering delving into the world of genre literature, you may well want to know which genres are the most popular - and which make the most money? With the increase in popularity of e-books, self-published authors now account for 20% of sales in the genre market - so this question isn't just one for the industry people. Now, it's relevant for any budding author with an internet connection! So, we've collated information on leading authors' earnings and reports of industry trends to bring you this list of the 5 most valuable, highest-earning genres in the book business - according to the Romance Writer's of America Association's reported figures of Simba Information Estimates.

5. Horror ($79.6 million)

With genre leader Stephen King said to have a net profit of $400 million and Dean Koontz with $125 million, horror's clearly a popular genre - but it's undeniably a smaller niche than some of the popular genres, valued at under $80 million. Readers enjoy being scared and they're loyal to their favourites, which is perhaps why King and Koontz - although having both written out of the genre - have been particularly prolific writers, each releasing fifty plus novels throughout the course of their career.

King generally publishes at least one book every year, including genre classics like 'The Shining', 'Salem's Lot', and 'It'. Horror can explore shocking subjects, often incorporating romance, fantasy and action along the way - but many people simply don't have the stomach for it, making this one of the less popular genres.

4. Science Fiction and Fantasy ($590.2 million)

With fantasy books such as 'Harry Potter', 'Lord of the Rings' and 'The Hunger Games' being turned into blockbusters, it stands to reason that this genre would be a money spinner. With an estimated $590.2 million, the fantasy genre owns huge names. Writers like Suzanne Collins and J.K. Rowling are topping rich lists, and these writers target a fanatical audience, often falling under the now hugely popular 'Young Adult' fiction umbrella. Fan sites and forums are rife with discussion on J.K. Rowling's books and the hunger for information is just as incessant among Hunger Games fans. And for the more mature male and female audience, there's the A Game of Thrones series by George R.R. Martin which also falls under this category and has an enormously popular television show serving to promote it.

The fact that fantasies are commonly written in sagas may have much to do with this genre's popularity. Fans of the fantasy world seem to enjoy staying with the characters for as long as possible, being left with cliffhangers. As long as there are more books, more movies and more fantastical worlds to be discovered this genre is likely to maintain its popularity.

3. Religious / Inspirational ($720 million)

It's common knowledge that the bible is the ultimate bestseller, topping record lists across the globe as the longest-standing, most-translated and widest-distributed book in the world. So, doubtless, that little number does a lot to boost the religious and inspirational genre. However, inspirational writers like Paulo Coelho - whose international bestsellers like The Alchemist have been hailed as transformative to the religious and inspirational genre - and Deepak Chopra, have kept the genre relevant in the 21st century. While many malign the 'self-help' section of their local bookstore, it's a booming industry and one that helps keeps the world of publishing afloat; to the tune of an estimated $720 million in revenue in 2012!

2. Crime / Mystery ($728.2 million)

Similar to fantasy, the crime and mystery genre is often built on sagas. Although the same set of characters might not be present in every part of a writer's series, there's usually a protagonist that the readers connect with and travel alongside. Readers become the Watson, working alongside Sherlock, dissecting every clue and racing to the end before moving onto the next case. Crime is a way into the minds of murderers, something forbidden but intriguing; and often, the 'true crime' stories are the most popular.

Some of this industry's big names include John Grisham with a staggering net worth of an estimate $200 million, and the deceased Stieg Larsson who gained $50 million with his 'The Girl With The Dragon Tattoo' series. In fact, the publishers of Larsson's books have hired a ghostwriter to continue the 'Dragon Tattoo' series, extending it to entertain readers and create more money.

1. Romance / Erotica ($1.44 billion)

Industry analyst the Bookseller has been reported as expounding, in their 2012 report, that erotica was 'cannibalising' the genre industry - at least in the United Kingdom. And what better example of this than the enormously popular 'Fifty Shades of Grey', which boomed its way into the publishing world and made E.L. James a star. To date, she's worth $60 million - having only written a trilogy, but with a lucrative film deal in the works. The trilogy, initially self-published by James online as Twilight fan fiction before it was picked up by a publisher, became known as "mom porn": It explored S&M through characters that women read and related to. The books seemed to epitomise escapism, and perhaps for this reason they became a phenomenon. The genre was ripe to be explored, and erotica showed a huge increase in Kindle purchases as people were too shy and embarrassed to buy the books in stores.

For similar reasons, romance novels contribute to the money-making power of the romantic / erotic genre. With the biggest name in the genre being Danielle Steel - with $610 million to her name - the genre is undeniably popular. Steel, herself, is known for publishing a number of books a year, sometimes working on five projects at a time. The writing of romance books is almost a science - certain story-lines need to be featured, the same kinds of endings and so on. Steel's books have been noted to have a format to them which readers enjoy. Readers of the romantic genre are similar to the erotic, in the sense that they want to stick to what they know but the romantic genre reader is less willing to move onto a different author, this is why Steel is so popular. Last year, the romance genre gained $1.438 billion and by the looks of things it's not going anywhere any time soon.