To cite the 'bookdown' package in publications use:

Xie Y (2019). bookdown: Authoring Books and Technical Documents with R Markdown. R package version 0.13, https://github.com/rstudio/bookdown.

Xie Y (2016). bookdown: Authoring Books and Technical Documents with R Markdown. Chapman and Hall/CRC, Boca Raton, Florida. ISBN 978-1138700109, https://github.com/rstudio/bookdown.

Corresponding BibTeX entries:

  @Manual{,
    title = {bookdown: Authoring Books and Technical Documents with R
      Markdown},
    author = {Yihui Xie},
    year = {2019},
    note = {R package version 0.13},
    url = {https://github.com/rstudio/bookdown},
  }
  @Book{,
    title = {bookdown: Authoring Books and Technical Documents with {R}
      Markdown},
    author = {Yihui Xie},
    publisher = {Chapman and Hall/CRC},
    address = {Boca Raton, Florida},
    year = {2016},
    note = {ISBN 978-1138700109},
    url = {https://github.com/rstudio/bookdown},
  }