The present chapter takes a social psychological approach to understanding hate groups and how hate groups use hate as a promotional tool and as an implement of aggression. As a promotional tool, hate groups use hate to attract new members to their organizations and to promote their beliefs to the mainstream public. Hate also serves as an incendiary, to fuel the emotions of their members, to incite them into action, and to wield against their targets. In this chapter we will attempt to explain why people hate and how they justify their hatred and resulting actions through a number of social psychological theories including realistic group conflict (Bonacich, 1972; Sherif et al., 1961/1988) relative deprivation (Catalono et al., 1993; Hepworth & West, 1988; Hovland & Sears, 1940), social identity theory (Abrams & Hogg, 1990; Festinger, 1954; Tajfel & Turner, 1986; Thoits & Virshup, 1997) and terror management (Pyszczynski, Solomon, & Greenberg, 1997; 2005; Solomon, Greenberg, & Pyszczynski, 1991; 2004).