Dystopian novels have been very popular in young adult literature over the last few years. The Hunger Games pretty much set the bar for what good dystopian literature is and pretty much set the genre on fire. :-)
So what makes a book a dystopian book? It's a book that is set in a dystopia - "an imaginary place where people lead dehumanized and often fearful lives" (Merriam-Webster, 2013). In these books, society (or the government) is usually the enemy, working against the main character's aims and desires. Dystopian novels tend to have dark themes like war, oppression, disease and disaster.
To learn more about Dystopian Literature visit the Dystopian Literature PathFinder.