This chapter presents the measurement approach we use to capture the variation in the CPSU membership rate in the regions of Russia. Specifically, we discuss how the data from the Congresses of the CPSU can be used to obtain the variation we are interested in; we also look at alternative sources of information available from archival sources and Soviet-era publications. The chapter also discusses how the heterogeneity of Russian regions will be used in our analysis to identify the effects of the Communist legacies, as well as introduces other datasets of the Communist era we apply in our study