To cite tmle in publications use:

Susan Gruber, Mark J. van der Laan (2012). tmle: An R Package for Targeted Maximum Likelihood Estimation. Journal of Statistical Software, 51(13), 1-35. URL http://www.jstatsoft.org/v51/i13/.

Corresponding BibTeX entry:

  @Article{,
    title = {{tmle}: An {R} Package for Targeted Maximum Likelihood
      Estimation},
    author = {Susan Gruber and Mark J. {van der Laan}},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {51},
    number = {13},
    pages = {1--35},
    url = {http://www.jstatsoft.org/v51/i13/},
  }