Privacy is the ability of individuals and groups to determine for themselves when, how and to what extent information about themselves is shared with others. At its extreme, privacy becomes anonymity when, for instance, a person uses it to conceal his or her true identity in order to cyber-bully someone else. Conversely, excessive privacy could also conceal the perpetrators of criminal, terrorist or computer hacking acts from law enforcement agencies.

Physical Physical privacy could be defined as preventing "intrusions into one's physical space or solitude“. This would include such concerns as: preventing intimate acts or hiding one's body from others for the purpose of modesty preventing unwelcome searching of one's personal possessions preventing unauthorized access to one's home, vehicle or man-cave medical privacy, the right to make fundamental medical decisions without governmental coercion or third party review, most widely applied to questions of contraception Organizational Governments agencies, corporations, groups/societies and other organizations may desire to keep their activities or secrets from being revealed to other organizations or individuals, adopting various security practices and controls in order to prevent this. Organizations may seek legal protection for their secrets. For example, a government administration may be able to invoke executive privilege or declares certain information to be classified, or a corporation might attempt to protect valuable proprietary information as trade secrets. Spiritual and intellectual The earliest legislative development of privacy rights began under British common law, which protected "only the physical interference of life and property." Its development from then on became "one of the most significant chapters in the history of privacy law." Privacy rights gradually expanded to include a "recognition of man's spiritual nature, of his feelings and his intellect." Eventually, the scope of those rights broadened even further to include a basic "right to be let alone," and the former definition of "property" would then comprise "every form of possession -- intangible, as well as tangible." By the late 19th century, interest in a "right to privacy" grew as a response to the growth of print media, especially newspapers.

Informational Information or data privacy refers to the evolving relationship between technology and the legal right to, or public expectation of privacy in the collection and sharing of data about one's self. Financial privacy, in which information about a person's financial transactions is guarded, is important for the avoidance of fraud including identity theft. Information about a person's purchases, for instance, can reveal a great deal about their preferences, places they have visited, their contacts, products (such as medications) they use, their activities and habits etc. Internet privacy is the ability to determine what information one reveals or withholds about oneself over the Internet, who has access to such information, and for what purposes one's information may or may not be used. For example, web users may be concerned to discover that many of the web sites which they visit collect, store, and possibly share personally identifiable information about them. Similarly, Internet users generally consider their s to be private and hence would be concerned if their was being accessed, read, stored or forwarded by third parties without their consent. Tools used to protect privacy on the Internet include encryption tools and anonymising services. Medical privacy allows a person to withhold their medical records and other information from others, perhaps because of fears that it might affect their insurance coverage or employment, or to avoid the embarrassment caused by revealing medical conditions or treatments. Political privacy has been a concern since voting systems emerged in ancient times. The secret ballot helps to ensure that voters cannot be coerced into voting in certain ways, since they can allocate their vote as they wish in the privacy and security of the voting booth while maintaining the anonymity of the vote. Secret ballots are nearly universal in modern democracy, and considered a basic right of citizenship, despite the difficulties that they cause (for example the inability to trace votes back to the corresponding voters increases the risk of someone stuffing additional fraudulent votes into the system: additional security controls are needed to minimize such risks).

Privacy uses the theory of natural rights, and generally responds to new information and communication technologies. In North America, Samuel D. Warren and Louis D. Brandeis wrote that privacy is the "right to be let alone" (Warren & Brandeis, 1890) focuses on protecting individuals. This citation was a response to recent technological developments, such as photography, and sensationalist journalism, also known as yellow journalism. Warren and Brandeis declared that information which was previously hidden and private could now be "shouted from the rooftops." Privacy rights are inherently intertwined with information technology. In his widely cited dissenting opinion in Olmstead v. United States (1928), Brandeis relied on thoughts he developed in his Harvard Law Review article in But in his dissent, he now changed the focus whereby he urged making personal privacy matters more relevant to constitutional law, going so far as saying "the government [was] identified... as a potential privacy invader." He writes, "Discovery and invention have made it possible for the Government, by means far more effective than stretching upon the rack, to obtain disclosure in court of what is whispered in the closet." At that time, telephones were often community assets, with shared party lines and the potentially nosey human operators. By the time of Katz, in 1967, telephones had become personal devices with lines not shared across homes and switching was electro-mechanical. In the 1970s, new computing and recording technologies began to raise concerns about privacy, resulting in the Fair Information Practice Principles.

Privacy law is the area of law concerning the protecting and preserving of privacy rights of individuals. While there is no universally accepted privacy law among all countries, some organizations promote certain concepts be enforced by individual countries. Privacy on the Internet There are many means to protect one's privacy on the internet. For example s can be encrypted and anonymizing proxies or anonymizing networks like I2P and Tor can be used to prevent the internet service providers from knowing which sites one visits and with whom one communicates. Privacy by Design The principle of Privacy by Design states that privacy and data protection are embedded throughout the entire life cycle of technologies, from the early design stage to their deployment, use and ultimate disposal.