Preventive detention refers to the act of detaining a person not for an offense already committed but to prevent the possibility of that person committing an offense in the future. The objective of preventive detention is not punishment but the prevention of activities that may threaten national security public order or social stability.

Under ordinary criminal law a person is arrested only after an offense has been committed or when there is sufficient evidence of criminal involvement. In contrast preventive detention is based on anticipation or suspicion that a person may act in a manner prejudicial to the security of the state maintenance of public order or essential supplies and services.

The Indian Constitution provides for preventive detention under Article 22. Normally a detained person has several safeguards such as the right to be informed of the grounds of arrest the right to consult a legal practitioner and the right to be produced before a magistrate within twenty four hours. However in cases of preventive detention some of these safeguards are restricted.

At the same time the Constitution also lays down certain protections against misuse of preventive detention. A person cannot be detained for more than three months unless an advisory board consisting of qualified judges approves the detention. The detaining authority must communicate the grounds of detention to the person so that a representation can be made against it.

Preventive detention laws are generally invoked in matters relating to national security public order foreign affairs and the maintenance of essential supplies. In independent India laws such as the Preventive Detention Act 1950 were enacted and various states have also passed similar legislation.

In recent years preventive detention has been a subject of debate due to concerns about its impact on personal liberty. Courts have repeatedly emphasized that preventive detention is an exceptional measure and should be used sparingly with strict adherence to constitutional safeguards.

In essence preventive detention is a legal mechanism designed to prevent potential threats to society but it must operate within clearly defined constitutional limits to protect individual freedom and democratic values.