Academic tenure is a guarantee of lifetime employment in an academic job, barring unforeseen and usually dramatic circumstances. Once a professor gains tenure, he or she becomes extremely difficult to remove from the position. Tenure has been widely criticized from both within the academic community and without, although there are certainly some solid reasons to offer academic tenure to notable professors. Many countries have reformed their tenure systems to reflect changing ideas about tenure and the nature of academic employment.
As a general rule, academic tenure is offered to instructors in senior positions. Until tenure is offered, professors are hired on a contract basis, which means that they could be released at any time. With tenure often come benefits such as a better office, health care benefits, larger payments into retirement accounts, and access to various perks at the university. Tenure is granted after a careful review of the candidate which is supposed to include teaching, publication history, research history, and a variety of other facets of the professor's performance.
In fact, tenure review sometimes focuses just on a professor's ability to get grants and get published, with the university looking for professors who will add to the endowment and prestige of the institution. As a result, sometimes shoddy professors get tenure, simply because they know how to assemble an appealing tenure application, and high-quality professors who are not as involved in academia may be overlooked.
The primary justification for academic tenure is academic freedom. Because tenured professors cannot be fired or released without very sound reasons, they usually feel freer to express themselves. Tenured professors are willing to speak out, to conduct controversial research, and to question conventional wisdom. Professors without tenure may feel pressured to toe the party line in order to keep their jobs. Since many universities claim to value academic freedom and the freedom of expression, academic tenure is ostensibly used to support such freedoms.
Job security is also a very important issue with many professional unions, and in some cases, unions may pressure universities to offer tenure. A union professor may only be able to work so many years on contract, for example, forcing the university to offer tenure or release the professor. This strategy can backfire, of course, because a university may decide that releasing the professor is in its best interest.
There are a number of valid criticisms of academic tenure. Tenured professors often teach less, confident that they can take on a smaller course load and keep their jobs. They may also offer less support to students, and some are criticized as bad or lazy teachers. Tenure also has a chilling effect on academic freedom for non-tenured professors, who try not to rock the boat until they get tenure. Tenured professors also tend to be expensive to maintain, so if they don't “earn their keep” with grants and prestigious publications, they can become white elephants.