Hazard ratios (HRs) are used commonly to report results from randomized clinical trials in oncology. However, they remain one of the most perplexing concepts for clinicians. A good understanding of HRs is needed to effectively interpret the medical literature to make important treatment decisions. This article provides clear guidelines to clinicians about how to appropriately interpret HRs. While this article focuses on the commonly used methods, the authors acknowledge that other statistical methods exist for analyzing survival data.