My good friend Danilo Freire and I have just finished a little R data package, called prisonbrief. We hope that it will be useful for R users, particularly researchers in the area, since this is still a much understudied topic. Why does prison population change? In many countries, it is rising, and has been for some time, and the determinants of this rise are still not well understood. All the data in the package come from the fantastic World Prison Brief website – we thank them for making these data available.