Several emerging wireline and wireless access network technologies exhibit asymmetry in their network characteristics. For instance, cable modem networks exhibit significant bandwidth asymmetry, while packet radio networks exhibit media access asymmetry. A high degree of asymmetry can have an adverse effect on the performance of feedback-based transport protocols. In this article we study the effects of bandwidth and media access asymmetry on the performance of the TCP protocol. We identify the fundamental reasons for the mismatch between TCP and asymmetric networks, and then present several techniques to address this problem.