Narrative nonfiction, also called literary journalism, blurs the lines between fiction and nonfiction writing. That's not to say there's any fiction involved in narrative nonfiction; it still has to hold to journalistic standards as far as facts are concerned. However, the narrative nonfiction writer utilizes many techniques used by fiction writers and applies them to a true story in order to make it a more engrossing read -- techniques such as building strong characters, setting detailed scenes, and using plot and character arcs to build tension within a story. A classic example of narrative nonfiction is Truman Capote's "In Cold Blood," a true account of the murders of a Kansas family told in novel form from the point of view of the writer as an investigator into the crimes and their aftermath. Other narrative nonfiction genres include biography and autobiography, memoir and personal essay.
Expository writing could also be called informative writing. This form of nonfiction's central purpose is to relay facts from the writer to the reader through meticulous research. Expository writing must be clear, organized and exhibit strong detail, with no opinion or editorializing from the writer. Scientific discourse, technical writing and factual essays are considered expository writing, along with news writing. This type of writing could be considered nonfiction in the purest sense of the term because it is the polar opposite of fiction.
A writer who argues a position or takes a side on an issue uses persuasive writing to get his or her point across. This type of writing is visible every day in the Op-Ed section of the newspaper. Persuasive writing mixes factual assertions with persuasive rhetoric and logical arguments to sway readers to one side of an issue. Political speeches and law documents are examples of persuasive nonfiction writing, as is any article or book that uses facts to back up a strong point of view.
Descriptive nonfiction brings a little bit of poetry to nonfiction writing, using sensory details and vivid, colorful language to bring real places, events and people to life. Any nonfiction writer that uses figurative, elaborate language and rich detail to better portray a scene is using descriptive writing, but certain genres use it almost exclusively. Nature writing is an example of this because accurate and powerful language is needed to properly convey the scale and splendor of the natural world. Travel writing and field guides are also genres that fall under the label of descriptive nonfiction.