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 Montana (MT), burglary is defined under Montana Code Annotated 45-6-204. The statute outlines that a person commits the offense of burglary if they knowingly enter or remain unlawfully in an occupied structure with the intent to commit a felony therein. The term 'occupied structure' is broadly defined and can include any building, vehicle, or other place suitable for human occupancy, whether or not a person is actually present. Montana law does not require breaking and entering; simply entering or remaining unlawfully with the requisite intent is sufficient. The offense is classified as a felony, and the severity of the punishment can vary depending on factors such as whether the burglary involved a residence (habitation) or another type of building, and whether a weapon was used or bodily injury occurred during the commission of the crime. Burglary of a residence is generally treated as a more serious crime and carries greater penalties. It's important to note that specific circumstances of the burglary can lead to enhanced charges or penalties, and Montana may have additional statutes that address related offenses such as criminal trespass or theft.