Pajek is an open source Windows program for analysis and visualization of large networks having some thousands or even millions of vertices. In Slovenian language the word pajek means spider. Pajek started development in November 1996. Pajek is implemented in Delphi (Pascal).
The main motivation for development of Pajek was the observation that there exist several sources of large networks that are already in machine-readable form. Pajek should provide tools for analysis and visualization of such networks: collaboration networks, organic molecule in chemistry, protein-receptor interaction networks, genealogies, Internet networks, citation networks, diffusion (AIDS, news, innovations) networks, data-mining (2-mode networks), etc.