The present study introduces the concept of Siege Mentality which denotes a mental state in which group members hold a central belief that the rest of the world has negative behavioral intentions toward them. Two scales were constructed to assess the level of Siege Mentality among a group of Israeli students: The General Siege Mentality Scale (GSMS) and the Israeli Siege Mentality Scale (ISMS). A series of analyses showed that Siege Mentality is a unique construct different from paranoid tendency and ethnocentrism, and that the two scales (GSMS and ISMS) assess a similar construct. Finally, the results show that Siege Mentality is the best predicted by the hawkish orientation regarding the IsraeliArab conflict.