Beijing Transportation Smart Card?

Well, I know lots of places you can purchase the card. Such as these:
1. no. 45, Fuxingmen Inner Street;
2. no. 17, Taipingqiao Street, Xicheng District;
3. no. 5, East Street, ZHushikou, Dongcheng District.
In a word, you can purchase the card in almost all the China Citic Bank branches in the city. Or in some subway stations, such as BJ Zoo, Zhongguancun, Anheqiao North, or The National Library, you can also purchase the card.

There are different kinds of buses in the city. For some of them, one just needs to stamp the card once, thus several people can use the same one card. For the others, one needs to stamp the card twice when he get on and get off. So one card can only be used by one person. Besides, passengers are not allowed to share cards in the subway. So for your convenience, it is suggested to purchase a card for each person.