I present and describe a new software package in the R statistical programming environment for dendrochronology. R is considered the world's pre-eminent open-source statistical computing environment where users can contribute packages, which are freely available on the Internet. The dendrochronology program library in R (dplR) is able to read standard decadal-format files and allows users to perform several standard analyses including interactive detrending, chronology building, and the calculation of standard descriptive statistics. The package can also produce a variety of publication quality plots. The dplR package should make it easier for dendrochronologists to take advantage of R and use it as their primary analytic environment.