To cite geepack in publications use:

Fine, J.~P., Yan, J., and Kosorok, M.~R. Temporal Process Regression Biometrika, 91, pp683--703.
Yan, J. & Fine, J.P. (2004) Estimating Equations for Association Structures Statistics in Medicine, 23, pp859--880.

Corresponding BibTeX entries:

  @Article{,
    title = {Temporal Process Regression},
    author = {Jason P. Fine and Jun Yan and Michael R. Kosorok},
    year = {2004},
    journal = {Biometrika},
    volume = {91},
    pages = {683--703},
  }
  @Article{,
    title = {Estimating Equations for Association Structures},
    author = {Jun Yan and Jason P. Fine},
    year = {2004},
    journal = {Statistics in Medicine},
    volume = {23},
    pages = {859--880},
  }