A gatekeeper is a person who controls access to something, for example via a city gate. In the late 20th century the term came into metaphorical use, referring to individuals who decide whether a given message will be distributed by a mass medium.
Gatekeepers serve in various roles including academic admissions, financial advising, and news editing. An academic admissions officer might review students' qualifications based on criteria like test scores, race, social class, grades, family connections, and even athletic ability. Where this internal gatekeeping role is unwanted, open admissions can externalize it.
A news editor selects stories for publication based on his or her organization's specific criteria, e.g., importance and relevance to their readership. For example, a presidential resignation would be on the front page of a newspaper but likely not a celebrity break-up (unless the paper was of the gossip variety).
Kurt Lewin was the first to identify the word gatekeeping. It was first mentioned in his book, Forces Behind Food Habits and Methods of Change. He first applied the concept to the food chain using the example of a female being the person deciding what food is placed on the dinner table. After exploring this idea he started to add to the gating process and how it can change the communication channels. The first person to turn Lewin’s words into a journalism idea was David Manning White in the 1950’s. Then in the 1970’s ideas about the influence of gatekeepers and their decisions were further developed by Maxwell McCombs and Donald Shaw in their construction of agenda setting theory. 
Academic peer review
Peer review is a practice widely used by specialized journals that publish articles reporting new research, new discoveries, or new analyses in a specific academic field or area of focus. Journal editors ask one or more subject matter experts deemed to be "peers" of an article's author or authors to assess an article's suitability for publication in the journal. Notwithstanding the fact that the intent of peer review is to insure suitability and editorial quality, issues of preference or exclusion of articles are raised from time to time relating to the intellectual prejudices, career rivalries, or other biases of the journal editors or peer reviewers.
For example, climate scientist Judith Curry discussed what she sees as gatekeeping behavior at Geophysical Research Letters, in rejecting a 2010 manuscript, "Assessing the consistency between short-term global temperature trends in observations and climate model projects," by Patrick J. Michaels, John Christy, Lucia Liljegren, James Annan, and other coauthors:  "I asked to see the reviews. I suspected gatekeeping by the editor and bias against the skeptical authors by the editor and reviewers." Unusually, James Annan was a first-round reviewer, and "signed on as a co-author after helping them solve some issues noted in the first set of reviews. The second round of review consisted of 4 reviewers, none of which supported publication." Curry concluded that, "Three years later, it seems pretty obvious and widely acknowledged that climate models have been unable to correctly capture the earth’s surface temperature evolution over the past several decades." 
Credentialing is the practice of evidencing suitability for engaging in a profession or for employability through documentation of demonstrated competency or experience, completion of education or training, or other criteria as specified by a credentialing authority. The documentation provided by the authority are known as "credentials", and may be in the form of a license, certificate of competency, a diploma, a teaching credential, a board certification, or a similar document. Credentialism refers to the practice of relying on credentials to prove the suitability of a professional person or a skilled employee to be assigned the responsibilities of professional engagement or employment.
Internet search engines
-  New York Times: "For Science's Gatekeepers, a Credibility Gap"
- Draft paper by Michaels et al., 2010
- Peer review: the skeptic filter by Judith Curry, September 19, 2013
-  www.timesandseasons.org, "Credentialism is Cruelty"
-  The British Journal of Social Work, "A Closed Profession?—Recruitment to Social Work "
-  www.wired.com, "Google Bows to Chinese Censorship"