The press and other media constantly report news stories about dangerous chemicals in the environment, miracle cures, the safety of therapeutic treatments, and potential cancer-causing agents. But what exactly is actually meant by "increased risk"-should we worry if we are told that we are at twice the risk of developing an illness? And how do we interpret "reduced risk" to properly assess the benefits of noisily touted dietary supplements? Demonstrating the difficulty of separating the hype from the hypothesis, noted epidemiologist Michael Bracken clearly communicates how clinical epidemiology works. Using everyday terms, Bracken describes how professional scientists approach questions of disease causation and therapeutic efficacy to provide readers with the tools to help them understand whether warnings of environmental risk are truly warranted, or if claims of therapeutic benefit are justified.