Burglary is generally the unlawful entry of a building or structure to commit a felony criminal offense (crime), theft, or assault. The definition of burglary varies from state to state (and in the federal system), and some states have different degrees of severity of the burglary offense, depending on the nature of the unlawful entry (type of building or structure), the intended purpose, and the illegal action taken by the defendant once inside the building or structure. In some states, breaking into an automobile, a coin-operated machine, or an ATM (automated teller machine) with the intent to commit a theft may also constitute the crime of burglary.

A defendant generally commits the offense of burglary of a building or habitation (1) by entering a private habitation or any part of a building that was not open to the public, (2) without the consent of the owner, and (3) with the intent to commit a felony, theft, or assault.

A defendant may also commit the offense of burglary of a building or habitation by entering with consent, but remaining hidden with the intent to commit a felony, theft, or assault—or entering with consent and attempting to commit a felony, theft, or assault, or actually committing a felony, theft, or assault.

Some states make a distinction between burglary of a habitation (a place used for overnight accommodations) and burglary of a building that is not a habitation (home). Burglary of a habitation is usually treated as a more serious offense with greater penalties.

In New York, burglary is defined under the New York Penal Law Section 140.20 to 140.30 and is classified into three degrees. Third-degree burglary (NY Penal Law § 140.20) is the unlawful entry into a building with intent to commit a crime therein, without the use of force against a person. Second-degree burglary (NY Penal Law § 140.25) involves the same elements but becomes more severe if the building is a dwelling, or if the defendant carries a weapon, injures someone, or displays what appears to be a firearm. First-degree burglary (NY Penal Law § 140.30) is the most serious and involves entering a dwelling with the same intent and either causing physical injury to a non-participant, using or threatening to use a dangerous instrument, or displaying what appears to be a firearm. The distinction between habitation and other buildings is significant in New York, with habitation burglaries typically facing harsher penalties. Additionally, New York law recognizes the concept of 'remaining unlawfully' where a person enters legally but then remains on the premises without permission and with the intent to commit a crime.