Arson is the crime of willfully and deliberately setting fire to or charring property. Though the act typically involves buildings, the term can also refer to the intentional burning of other things, such as motor vehicles, watercraft, or forests. The crime is typically classified as a felony, with instances involving a greater degree of risk to human life or property carrying a stricter penalty. Arson which results in death can be further prosecuted as manslaughter or murder. A common motive for arson is to commit insurance fraud. In such cases, a person destroys their own property by burning it and then lies about the cause in order to collect against their insurance policy.

A person who commits arson is referred to as an arsonist, or a serial arsonist if committed several times. Arsonists normally use an accelerant (such as gasoline or kerosene) to ignite, propel and directionalize fires, and the detection and identification of ignitable liquid residues (ILR’s) is an important part of fire investigations. Pyromania is an impulse control disorder characterized by the pathological setting of fires. Most acts of arson are not committed by pyromaniacs.

Blackmail is an act of coercion using the threat of revealing or publicizing either substantially true or false information about a person or people unless certain demands are met. It is often damaging information, and it may be revealed to family members or associates rather than to the general public. These acts can also involve using threats of physical, mental or emotional harm, or of criminal prosecution, against the victim or someone close to the victim. It is normally carried out for personal gain, most commonly of position, money, or property. It is also used, sometimes by state agencies, to exert influence; this was a common Soviet practice, so much so that the term "kompromat", transliterated from Russian, is often used for compromising material used to exert control.

Blackmail may also be considered a form of extortion. Although the two are generally synonymous, extortion is the taking of personal property by threat of future harm. Blackmail is the use of threat to prevent another from engaging in a lawful occupation and writing libelous letters or letters that provoke a breach of the peace, as well as use of intimidation for purposes of collecting an unpaid debt.

In many jurisdictions, blackmail is a statutory offense, often criminal, carrying punitive sanctions for convicted perpetrators. Blackmail is the name of a statutory offense in the United States, England and Wales, and Australia, and has been used as a convenient way of referring to certain other offenses, but was not a term used in English law until 1968.

Blackmail was originally a term from the Scottish Borders meaning payments rendered in exchange for protection from thieves and marauders. The "mail" part of blackmail derives from Middle English male meaning "rent or tribute". This tribute (male or reditus) was paid in goods or labor; hence "blackmail". Alternatively, it may be derived from two Scottish Gaelic words blathaich - to protect; and mal - tribute or payment.