To cite tm in publications use:

Stefan Theussl, Ingo Feinerer, Kurt Hornik (2012). A tm Plug-In for Distributed Text Mining in R. Journal of Statistical Software, 51(5), 1-31. URL http://www.jstatsoft.org/v51/i05/.

Corresponding BibTeX entry:

  @Article{,
    title = {A {tm} Plug-In for Distributed Text Mining in {R}},
    author = {Stefan Theu{\ss}l and Ingo Feinerer and Kurt Hornik},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {51},
    number = {5},
    pages = {1--31},
    url = {http://www.jstatsoft.org/v51/i05/},
  }