To cite segmented in publications use:

Vito M. R. Muggeo (2003). Estimating regression models with unknown break-points. Statistics in Medicine, 22, 3055-3071.
Vito M. R. Muggeo (2008). segmented: an R Package to Fit Regression Models with Broken-Line Relationships. R News, 8/1, 20-25. URL http://cran.r-project.org/doc/Rnews/.

Corresponding BibTeX entries:

  @Article{,
    title = {Estimating regression models with unknown break-points.},
    author = {Vito M.R. Muggeo},
    journal = {Statistics in Medicine},
    year = {2003},
    volume = {22},
    pages = {3055--3071},
  }
  @Article{,
    title = {segmented: an R Package to Fit Regression Models with
      Broken-Line Relationships.},
    author = {Vito M.R. Muggeo},
    journal = {R News},
    year = {2008},
    volume = {8},
    number = {1},
    pages = {20--25},
    url = {http://cran.r-project.org/doc/Rnews/},
  }