This article studies the structure of jihadist terrorism in the West from the perspective of the existence or absence of links between grassroots militants and organizations such as Al Qaeda Central and its regional affiliates. It undertakes a comprehensive case study of jihadist militancy in a European country (Spain) over a period of almost two decades, from 1995 until December 2013. The study analyzes the results of 64 antiterrorist operations carried out during this time.