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 Massachusetts, burglary is defined under Massachusetts General Laws Chapter 266, Section 14 as the breaking and entering of a dwelling house at night with the intent to commit a felony. The law distinguishes between burglary of a dwelling house and other types of structures. Burglary of a dwelling is considered more serious and carries stiffer penalties, including the possibility of life imprisonment if the burglar is armed and/or causes injury. The statute also covers situations where an individual enters without breaking, remains in the dwelling house surreptitiously, or enters with consent but then hides or remains with the intent to commit a felony. Burglary during the daytime or of a building other than a dwelling is also criminalized but is generally treated with less severity. The intent to commit a felony, theft, or assault is a critical element of the crime, and the penalties can vary based on factors such as whether the burglar was armed and whether the burglary resulted in a confrontation or injury.