OpeOpen Government Websites are a different perspective for presenting government information. In the Mexican case, it is mandatory by law since 2002 to present some government data through Websites. Despite this strong impulse of transparency, there is not enough measurement for the success or the failure of this novel practice. This chapter analyses data collected from a benchmarking of three year measures of open government portals during 2007, 2009, and 2010. From this data, three success factors are identified: trust, search engine, and legal issues. The success factors for open government portals are a contribution that must be verified by further research. This chapter is organized in seven sections. In the first section is the introduction of open government and the background of the Mexican case; the second section presents a literature review about open government and success factors; the third section describes the methodology of the open government portals measurement during 2008-2010; the fourth section discusses the results of this benchmarking and identifies three success factors: trust, search engine, and legal component; the fifth section describes these three findings and provides some recommendations for practitioners; the sixth section discusses the limitations of success factors and the limitations of this kind of research; a final section of future research presents some research paths, and a final conclusion section closes the chapter with a summary of findings and discussion.