Transit police (also known as transport police, railway police, railroad police and several other terms) are specialized police agencies employed either by a common carrier (a transit district, railway, railroad, bus line, or any other mass transit provider) or a municipality, county, district, or state. Transit law enforcement services may also be provided by a specialized unit within a larger local law enforcement agency. Their mandate is to prevent and investigate all crime committed against the carrier or its passengers, as well as crime incidentally committed on – and sometimes around – the carrier's property.