This title was first published in 2000. Nationalism and the national question have represented a problem since the early years of the 19th century. Understanding these phenomena represents a challenge for political science, because "the nation" is not a natural phenomenon, rather it is the consequence of nationalism. Attempts to reduce nationalism to one or several factors have been unsuccessful; it has multiple factors that are variable in space and time. Nationalism is a problem of beliefs and conscience linked to the historical action of nationalist groups. A second difficulty derives from the distinction between nationalism of the dominant and nationalism of the oppressed. The majority of political theorists now believe that these centre and periphery nationalisms are different and therefore adversaries. Using first-hand experience of Basque separatism as a starting point, the author adds to it with the main manifestations of this phenomenon around the world.