Urban fantasy is a broad subgenre of fantasy that blends contemporary fantasy with elements of crime fiction or noir. Urban fantasy is usually grittier than other contemporary fantasy books, and is set at least partially in a city or an urban environment.
Some urban fantasy books closely resemble paranormal romance, but in paranormal romance the love story arc is paramount. In some cases, the differences between the two subgenres are almost indistinguishable, as in Jeaniene Frost's bestselling Night Huntress series. This Book Country blog post elaborates on what separates urban fantasy from other genres.
Urban fantasy came into its own in the 1990s, and has enjoyed a peak in recent years. At the moment, the book market is oversaturated with established urban fantasy series, making it harder for new writers to make a name for themselves.
Laurell K. Hamilton is considered the first breakout urban fantasy writer. The works of Charlaine Harris and Jim Butcher are modern classics.