Subway 地铁
Transportation: Subway

You can also purchase a public transportation card at the subway ticket windows, which you can use at all the subways, bus routes and in all of the taxis. The card is free, but you must pay a 30RMB deposit that you will get back when you return the card. During rush hour this can make a huge difference, as lines can be really long at the ticket windows.
A word of warning: The Shanghai metro system is expanding, but is currently still only 5 lines that transport a HUGE number of people everyday. During rush hour these trains can be stiflingly crowded. The crowds can certainly reach a level of unbearable for those who are even somewhat claustrophobic. Actually, experiencing the metro at these hours could theoretically cause one to develop claustrophobia. I’ve personally witness a train that was fuller than that of Tokyo, which I had previously believed to be impossible.
Links:
A map of the Shanghai Subway
The official Shanghai Metro Website (no English)