What is the best way to get from BWI airport (Baltimore, MD) to Potomac, MD.?

I'd prefer to take public transportation (rail, metro), but not sure which transit system (or combination of) will accomplish this task.

Take the Marc to Union station. From there get on the metro and take the red line towards Shady Grove. You can get off at either Medical Center or Grosvenor-Strathmore, whichever is closer to your destination. From the metro you'd either have to take a cab, have someone pick you up, or see what buses go close to where in Potomac you are going.

Your best bet is to follow the directions listed by the previous poster (I fly out of BWI all the time). The next best option is to take the super shuttle shared van. It's about $35 and they'll drop you off right at your door. go to http://www.supershuttle.com/

Alternate source of transportation...the "Super Shuttle". It's cheaper than a cab.