To cite partykit in publications use:

Torsten Hothorn, Achim Zeileis (2015). partykit: A Modular Toolkit for Recursive Partytioning in R. Journal of Machine Learning Research, 16, 3905-3909. URL http://jmlr.org/papers/v16/hothorn15a.html

If ctree() is used additionally cite:

Torsten Hothorn, Kurt Hornik and Achim Zeileis (2006). Unbiased Recursive Partitioning: A Conditional Inference Framework. Journal of Computational and Graphical Statistics, 15(3), 651--674,<doi:10.1198/106186006X133933>

If mob() is used additionally cite:

Achim Zeileis, Torsten Hothorn and Kurt Hornik (2008). Model-Based Recursive Partitioning. Journal of Computational and Graphical Statistics, 17(2), 492--514,<doi:10.1198/106186008X319331>

Corresponding BibTeX entries:

  @Article{,
    title = {{partykit}: A Modular Toolkit for Recursive Partytioning
      in {R}},
    author = {Torsten Hothorn and Achim Zeileis},
    journal = {Journal of Machine Learning Research},
    year = {2015},
    volume = {16},
    pages = {3905-3909},
    url = {http://jmlr.org/papers/v16/hothorn15a.html},
  }
  @Article{,
    title = {Unbiased Recursive Partitioning: A Conditional Inference
      Framework},
    author = {Torsten Hothorn and Kurt Hornik and Achim Zeileis},
    journal = {Journal of Computational and Graphical Statistics},
    year = {2006},
    volume = {15},
    number = {3},
    doi = {10.1198/106186006X133933},
    pages = {651--674},
  }
  @Article{,
    title = {Model-Based Recursive Partitioning},
    author = {Achim Zeileis and Torsten Hothorn and Kurt Hornik},
    journal = {Journal of Computational and Graphical Statistics},
    year = {2008},
    volume = {17},
    number = {2},
    doi = {10.1198/106186008X319331},
    pages = {492--514},
  }