Historically, SLEIPNER was conceived of and conceptualized in the Stockholm Laboratory for Developmental Science by Lars Bergman and Bassam EI Khouri. It has gradually evolved during the last 12 years with the program code written by EI Khouri. The package is a collection of modules implementing methods of analysis that were carefully chosen to form a self-contained and empirically grounded toolbox for handling longitudinal data within the person-oriented paradigm. As the background concepts evolved and the need grew for special tailored tools for conducting the analysis, more modules were constructed. The version of SLEIPNER presented here (version 2.1) now comprises 16 distinct modules.