To cite depmixS4 in publications use:

Ingmar Visser, Maarten Speekenbrink (2010). depmixS4: An R Package for Hidden Markov Models. Journal of Statistical Software, 36(7), 1-21. URL http://www.jstatsoft.org/v36/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {{depmixS4}: An {R} Package for Hidden Markov Models},
    author = {Ingmar Visser and Maarten Speekenbrink},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {36},
    number = {7},
    pages = {1--21},
    url = {http://www.jstatsoft.org/v36/i07/},
  }