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.

In Montana (MT), burglary is defined under Montana Code Annotated 2021, Section 45-6-204. The statute describes burglary as knowingly entering or remaining unlawfully in an occupied structure with the intent to commit a felony or a theft therein. Montana law does not require the actual commission of the intended crime for an act to be considered burglary; the intent to commit the crime is sufficient. The state categorizes burglary as a felony offense, and the severity of the charge can be influenced by factors such as whether the burglary occurred at night or if a weapon was involved. Additionally, Montana law recognizes 'home invasion burglary' as a more serious form of burglary, which occurs when an individual unlawfully enters an occupied residence. While the state's burglary statute primarily focuses on buildings or structures, other statutes address illegal entry into motor vehicles or other property with the intent to steal, which may be prosecuted under different criminal charges such as theft or criminal mischief.