It is critical to understand WWW latency in order to design better HTTP protocols. In this paper we characterize Web response time and examine effects of proxy caching on response time. We show that at least a quarter of the total elapsed time is spent in setting up TCP connections. We also characterize the effect of a user's network bandwidth on response time. Average connection time from a client via a 33.6 K modem is two times longer than that from a client via switched Ethernet. Contrary to the typical thought about Web proxy caching, this study finds that a single stand alone proxy cache does not always reduce response time. Implications of these results to the HTTP-NG protocol and Web application design also are discussed in the paper.