Secondary education continues to expand rapidly worldwide. Equally important is its diversification. The present paper contends that the diversification of secondary education, while acknowledged, is not well studied. Despite the widespread expansion of secondary education in different world regions, the information available to researchers--and policy makers--for informed comparisons of secondary education systems has been, and remains, rather superficial and limited. The present paper compares the programmatic foci and contents of secondary education systems. It seeks to move beyond existing characterizations of secondary education, by reporting initial results from an International Bureau of Education-sponsored, cross-national study of secondary level programs, tracks and curricula. This study, while mainly limited to academic-oriented tracks, provides an empirical basis for comparing the diversification of secondary education systems. (Contains 12 tables and 14 footnotes.) [Additional funding for this report was provided by: the EFA Global Monitoring Report. An earlier version of this paper was prepared with the collaboration of Massimo Amadio for the publication: "Expanding Opportunities and Building Competencies for Young People: A New Agenda for Secondary Education." (Washington DC: World Bank, 2005). This is a slightly revised version of "La diversificacion en la educacion secundaria: Curriculos escolares desde la perspectiva comparada," "Profesorado: Revista de curriculum y formacion del profesorado" 10(1): 1-29, 2006; published by the University of Granada, Spain.]