The Surveillance, Epidemiology, and End Results (SEER) database is a publicly available, federally funded cancer reporting system that represents a collaboration between the US Centers for Disease Control and Prevention, the National Cancer Institute, and regional and state cancer registries.1 SEER data are national, with information from 18 states that represent all regions of the country. In contrast to other commonly used data sets (eg, the National Cancer Data Base), SEER is population-based, because local registries report information for all cancer cases within a specific region and/or defined racial/ethnic population. Given that SEER data is both a cancer reporting system and a research tool, we aim to present salient aspects of these data, strengths and limitations for analyses, and important statistical considerations.