This thesis is a study of the ideology and 'mentality' of the Seljuqs of Rum 473-641/1081-1243. It focuses on this little-known branch of the Seljuqs, whose rule in Anatolia lasted considerably longer than the Great Seljuq state further east. This study uses the few available Rum Seljuq primary sources in Persian and Arabic, as well as contemporary oriental Christian chronicles; it also draws on the evidence of coins and monumental inscriptions, where possible. Chapter one discusses the background of the Great Seljuqs, how they came into the Islamic world, bringing with them their centuries-old nomadic lifestyle and modes of thinking. This Chapter also analyses the way in which these Turkish nomadic chiefs were presented as Muslim rulers by the Arabic and Persian religious scholars and bureaucrats who served them. Chapter two discusses how the earliest Seljuq leaders in Anatolia from 473-500/1081-1107 conformed to traditional patterns of nomadic rule, and the period of interregnum and transition (500-551/1107-1156) during which the Seljuqs in Anatolia were dominated by the rival Turkish Danishmendid principality. Chapter three shows how the Rum Seljuq principality in Anatolia was transformed by the beginning of the thirteenth century into the Rum Seljuq sultanate. In chapter four the discussion focuses on the apogee of the dynasty under the rule of Kay Kawfis I (608-616/1211-1220) and Kay Qubadh I (616-634/1220-1237) where it may be argued that these two Seljuq sultans could justifiably be viewed as model Perso-Islamic rulers, although elements from their Turkish nomadic past remained. The appendix contains an analysis of the crucial relationship between the Rum Seluqs and their Byzantine neighbours during the period (473-576/1081-1180), arguing that a pattern of friendly co-existence was established between the Seljuq sultans and the Comneni emperors during these years. The thesis shows how ideology rather than mere military success helped to shape this important dynasty into a fully-fledged sultanate.