On campus, there are six shuttle bus routes: there's one going between the main campus and the east campus (School of Divinity), one that travels between the main campus and the west campus (Law School), one that roams over by the main campus and the Meridian dorm, one going between the main campus and the Slowe and Carver dorms, and one going between the main campus, the hospital, and the Metro station. The last one basically circulates throughout campus, picking up and dropping off students wherever they want to go.
When you want to step off campus and venture out into the city, your best bet is to take public transportation. The Metro runs from 5:30 a.m. to 12 a.m. on weekdays and from 6:30 a.m. to around 3 a.m. on weekends. The Metro can take you to all the city's museums and cultural spots, shops, restaurants, malls, and nighttime hotspots. Other possible transportation options include general car rental services, particularly the Zipcar system, a car rental company that caters to students with cars and is available at select Metro stations, Amtrak (for when you want to go out of town), the Marc train system, and the Virginia Railway Express, all of which not only serve locations outside of DC but also connect at DC's Union Station.