Secrecy or furtiveness is the practice of sharing information among a group of people, which can be as small as one person, while hiding it from all others. That which is kept hidden is known as the secret. Secrecy is often controversial. Many people claim that, at least in some situations, it is better for everyone if everyone knows all the facts—there should be no secrets. Many biologists also claim that, with possible exceptions, it is better for everyone if the spread of information from its origins is as slow as possible - there should be as much secrecy and privacy as possible. The closely allied, perhaps even synonymous notions of confidentiality and privacy are often considered virtues. Although this belief is held by many people, most argue that it is taken out of context. William Penn wrote, "It is wise not to seek a secret; and honest, not to reveal one."

Natural and sociological secrecy

Secrecy is built into biology. One reason for sexual reproduction and speciation may be to allow members of a species to share genetic improvements without those improvements becoming available to competitors. Animals, including humans (in some cases), conceal the location of their den or nest from predators. Humans attempt to consciously conceal aspects of themselves from others due to shame, or from fear of rejection, loss of acceptance, or loss of employment. On a deeper level, humans attempt to conceal aspects of their own self which they are not capable of incorporating psychologically into their conscious being. Families sometimes maintain "family secrets", obliging family members never discuss disagreeable issues concerning the family, either with those outside the family and sometimes even within the family. Many "family secrets" are maintained by using a mutually agreed-upon construct (an official family story) when speaking with outside members. Agreement to maintain the secret is often coerced through "shaming" and reference to family honor. The information may even be something as trivial as a recipe.

Keeping one's strategy secret is important in many aspects of game theory.

Secret sharing (anthropology)

In anthropology secret sharing is one way for men to establish traditional relations with other men. A commonly used Academic narrative that describes this kind of behavior is Joseph Conrad's The Secret Sharer. Another traditional way for men to establish such relations is through an exchange of women.

Government secrecy

Governments often attempt to conceal information from other governments and the public. These state secrets can include weapon designs, military plans, diplomatic negotiation tactics, and secrets obtained illicitly from others ("intelligence"). Most nations have some form of Official Secrets Act (the Espionage Act in the U.S.) and classify material according to the level of protection needed (hence the term "classified information"). An individual needs a security clearance for access and other protection methods, such as keeping documents in a safe, are stipulated.