Taxis are available in Baltimore 24 hours a day at all hotels and at the airport.  Several taxi companies work in the city, but one of the biggest is Yellow Transportation.  Their taxis are available by phone 24 hours a day at 410-685-1212. To check the taxi fare in advance, try using the Baltimore Taxi Fare Finder

Rental cars are available from all major US rental companies at the Baltimore/Washington International Airport (BWI) as well as in the city itself.  Car rental companies have offices in many hotels, while  Enterprise, and Budget  have several city locations.

BEWARE TAXI RIP OFFS..  Make sure the driver puts the meter on. Check and memorize the number of the cab, then compare it with your receipt. Check that the name of the business on the receipt matches the cab's company.