Health scientists increasingly use data from unequal-probability survey designs, either public-use data from national surveys such as NHANES and NLSY, or their own surveys, or from subsamples of existing cohorts or databases. Correct analysis of survey data requires appropriate software and an understanding of basic survey concepts, but is otherwise just like any data analysis. In this module we will cover the concepts of weights, clusters, and strata, and how to use the R survey package to conduct analyses.