“Emphasizes group process and intergroup relations.” (Andreassi, Desrochers & Thompson)
“A social psychological theory of identity formulation that privileges the role of large group identities in forming individuals’ concepts of self.” (Calhoun, 2003).
Hogg et al contrast Identity Theory (IT) (the focus of the Encyclopedia entry by Desrochers, Andreassi, and Thompson), and Social Identity Theory (SIT), which is a different theory with different origins, as can be seen by comparing definitions of IT by Hogg et al provided elsewhere in this entry, and the definition of SIT they provide below. They propose that SIT “is intended to be a social psychological theory of intergroup relations, group processes, and the social self. It has its origins in early work in Britain by Henri Tajfel on social factors in perception (e.g., Tajfel, 1959, 1969a) and on cognitive and social belief aspects of racism, prejudice, and discrimination (e.g., Tajfel, 1963, 1969b, 1970), but was developed and fully formulated in collaboration with John Turner and others in the mid- to late 1970s at the University of Bristol (e.g., Tajfel, 1974, 1978, 1982; Tajfel and Turner, 1979; J. C. Turner, 1982)…The basic idea is that a social category (e.g., nationality, political affiliation, sports team) into which one falls, and to which one feels one belongs, provides a definition of who one is in terms of the defining characteristics of the category-a self-definition that is a part of the self-concept” (p. 259). (Desrochers)

Desrochers, S., Andreassi, J., & Thompson, C.  (2002, August 14). Identity Theory, A Sloan Work and Family Encyclopedia Entry. Chestnut Hill, MA: Boston College. Social Identity Theory. (2002). In Craig Calhoun, (Ed.), Dictionary of the social sciences in politics and social sciences. UK: Oxford University Press, Inc. Internet Explorer. (16 June 2003). As defined by Desrochers citing Hogg, Terry White: Hogg, M., Terry, D. & White, K. (1995). A tale of two theories: A critical comparison of identity theory with social identity theory. Social Psychology Quarterly, 58, 255-269.