I just did this tour last month as part of a group arranged by my Senator. The previous poster is correct. Our tour was led by an intern but our group was small. (3 people) She also took us to places where the big groups don't go and we got to ride the underground subway back to the Hart Senate Office Building. In addition, you meet your tour guide at your Senator or Rep's office and you can leave any packages or backpacks behind. This is nice especially if you're doing any shopping beforehand. I don't know about you but I prefer to have my arms/back free when touring museums and the like. Too much weight makes me tired.