What is the difference between flow control and congestion control?

TCP's four congestion control algorithms include: slow start, congestion avoidance, fast retransmit, and fast recovery. Congestion control basically states that a network device can transmit only a certain number of packets and can not add more packets to a network until an acknowledgement is received. http://www.ecse.rpi.edu/Homepages/shivkuma/research/cong-papers.html has some good papers on the topic.

Flow control works by refusing new connections until congestion is resolved. In serial transmissions, Xon/Xoff is used for flow control. It is a handshaking mechanism that will keep a sender from sending data faster than a receiver can receive it.