Ideology has re-emerged as a vital topic of investigation in social psychology. This chapter proposes that political ideologies possess both a discursive superstructure and a functional substructure and that ideologies serve social psychological functions that may not be entirely rational but help to explain why individuals are drawn to them. System justification, it argues, is the ‘glue’ that holds the two dimensions of left–right ideology together. To vindicate and uphold traditional institutions and arrangements, the right defends existing inequalities as just (...) and necessary. To bring about a more equal state of affairs, the left is motivated to challenge existing institutions and practices. (shrink)