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 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 armed and unarmed burglary, as well as between burglary with and without the presence of people inside the dwelling. The severity of the charge and the potential penalties increase if the burglar is armed, if the burglary results in a confrontation, or if the burglar intentionally inflicts or attempts to inflict bodily injury. Massachusetts law also recognizes the burglary of a building other than a dwelling, such as a store or office, which is addressed under Section 20 of the same chapter. The intent to commit a felony remains a crucial element of the crime. Burglary of vehicles, ATMs, or coin-operated machines may fall under different statutes related to larceny or breaking and entering of a vehicle or other structure, rather than traditional burglary of a dwelling.