The examples and perspective in this article may not represent a worldwide view of the subject. (May 2015) (Learn how and when to remove this template message)
An op-ed, short for "opposite the editorial page", is a written prose piece typically published by a newspaper or magazine which expresses the opinion of an author usually not affiliated with the publication's editorial board. Op-eds are different from both editorials (opinion pieces submitted by editorial board members) and letters to the editor (opinion pieces submitted by readers).
The direct ancestor of the modern op-ed page was created in 1921 by Herbert Bayard Swope of The New York Evening World. When Swope took over as editor in 1920, he realized that the page opposite the editorials was "a catchall for book reviews, society boilerplate, and obituaries". He wrote:
It occurred to me that nothing is more interesting than opinion when opinion is interesting, so I devised a method of cleaning off the page opposite the editorial, which became the most important in America ... and thereon I decided to print opinions, ignoring facts.
Swope included only opinions by employees of his newspaper, leaving the "modern" op-ed page to be developed in 1970 under the direction of The New York Times editor John B. Oakes. The first op-ed page of The New York Times appeared on 21 September 1970. 
Writes media scholar Michael Socolow of Oakes' innovation:
The Times' effort synthesized various antecedents and editorial visions. Journalistic innovation is usually complex, and typically involves multiple external factors. The Times' op-ed page appeared in an era of democratizing cultural and political discourse and of economic distress for the company itself. The newspaper's executives developed a place for outside contributors with space reserved for sale at a premium rate for additional commentaries and other purposes.
Beginning in the 1930s, radio began to threaten print journalism, a process that was later accelerated by the rise of television. To combat this, major newspapers such as The New York Times and The Washington Post began including more openly subjective and opinionated journalism, adding more columns and increasing the extent of their op-ed pages.
A concern about how to clearly disclose the ties in the op-eds arises because the readers of the media cannot be expected to know all about the possible connections between op-eds, editors and interest groups funding some of them. In a letter to The New York Times, the lack of a clear declaration as to conflict of interest in op-eds was criticized by a group of U.S. journalists campaigning for more "op-ed transparency".