A ghostwriter is a person hired to write literary or journalistic works, speeches, or other texts that are credited to another person as the author. Celebrities, executives, participants in timely news stories, and political leaders often hire ghostwriters to draft or edit autobiographies, memoirs, magazine articles, or other written material.

A ghostwriter is expected to closely replicate the writing style and voice of an author's previous works while still providing new literary content. Memoir ghostwriters in particular pride themselves on "disappearing" into the persona of the credited author as a mark of craftsmanship. In music, ghostwriters are often used to write songs, lyrics, and instrumental pieces. Screenplay authors can also use ghostwriters to either edit or rewrite their scripts to improve them. Usually, there is a confidentiality clause in the contract between the ghostwriter and the credited author (or publisher) that obligates the former to remain anonymous, or obligates the latter to not reveal the ghostwriter. Sometimes the ghostwriter is acknowledged by the author or publisher for their writing services, euphemistically called a "researcher" or "research assistant", but often the ghostwriter is not credited.

Ghostwriting (or simply "ghosting") also occurs in other creative fields. Composers have long hired ghostwriters to help them to write musical pieces and songs; Wolfgang Amadeus Mozart is an example of a well-known composer who was paid to ghostwrite music for wealthy patrons. Ghosting also occurs in popular music. A pop music ghostwriter writes lyrics and a melody in the style of the credited musician. In hip hop music, the increasing use of ghostwriters by high-profile hip-hop stars has led to controversy. In the visual arts, it is not uncommon in both fine art and commercial art such as comics for a number of assistants to do work on a piece that is credited to a single artist; Andy Warhol engaged in this practice, supervising an assembly line silk screen process for his artwork. However, when credit is established for the writer, the acknowledgment of their contribution is public domain and the writer in question would not be considered a ghostwriter.

A consultant or career-switcher may pay a ghostwriter to write a book on a topic in their professional area, to establish or enhance credibility as an expert in their field. Public officials and politicians employ "correspondence officers" to respond to the large volume of official correspondence. A number of papal encyclicals have been written by ghostwriters. A controversial and scientifically unethical practice is medical ghostwriting, where biotech or pharmaceutical companies pay professional writers to produce papers and then recruit (via payment or as a perk) other scientists or physicians to attach their names to these articles before they are published in medical or scientific journals. Some university and college students hire ghostwriters from essay mills to write entrance essays, term papers, theses, and dissertations. This is largely considered unethical unless the actual ghostwriting work is just light editing.

Ghostwriters are hired for numerous reasons. In many cases, celebrities or public figures do not have the time, discipline, or writing skills to write and research a several hundred-page autobiography or "how-to" book. Even if a celebrity or public figure has the writing skills to pen a short article, they may not know how to structure and edit a several hundred-page book so that it is captivating and well-paced. In other cases, publishers use ghostwriters to increase the number of books that can be published each year under the name of well-known, highly marketable authors, or to quickly release a topical book that ties in with a recent or upcoming newsworthy event.

Ghostwriters will often spend from several months to a full year researching, writing, and editing non-fiction and fiction works for a client, and they are paid based on a price per hour, per word, or per page, with a flat fee, a percentage of the royalties of the sales, or some combination thereof. In 2013, literary agent Madeleine Morel stated that the average ghostwriter's advance for work for major book publishers was "between $40,000 and $70,000". These benchmark prices are mirrored approximately in the film industry by the Writers Guild, where a Minimum Basic Agreement gives a starting price for the screenplay writer of $37,073 (non-original screenplay, no treatment).

However, the recent shift into the digital age (15–20% world market share of books by 2015) has brought some changes, by opening newer markets that bring their own opportunities for authors and writers—especially on the more affordable side of the ghostwriting business. One such market is the shorter book, best represented at the moment by Amazon's Kindle Singles imprint: texts of 30,000 words and under. Such a length would have been much harder to sell before digital reader-technologies became widely available, but is now quite acceptable. Writers on the level of Ian McEwan have celebrated this recent change, mainly for artistic reasons.

As a consequence, the shorter format makes a project potentially more affordable for the client/author. Manhattan Literary, a ghostwriting company, states that "book projects on the shorter side, tailored to new markets like the Kindle Singles imprint and others (30,000–42,000 words) start at a cost of $15,000". And this shorter book appears to be here to stay. It was once financially impractical for publishers to produce such novella-length texts (they would have to charge too much); but this new market is, by 2015, already substantial and has been projected to be a solid part of the future of book publishing. So, with its appearance the starting price for the professional book writer has come down by about half, but only if this shorter format makes sense for the client.