Poortinga and colleagues (Poortinga and van de Vijver, 1987; Poortinga et al., 1987) introduced a metaphor for the process of explaining cross-cultural variance in psychology that has been one of the guiding principles in my work as a cross-cultural researcher. ‘Peeling the onion called culture’ refers to explaining proportions of cross-cultural variance accounted for by separate cultural variables analogous to removing the layers of an imaginary onion. The object of cross-cultural studies is to explain all variance until nothing is left to be explained. This chapter describes the empirical support that can be found for the various frameworks of cross-cultural differences, and evaluates the extent to which cross-cultural differences are systematic. Two fundamental questions as outlined in Chapter 1 (editors) are particularly relevant in the present chapter: What is the relationship between individual and culture, and what are methodological challenges to the field of cross-cultural psychology?

Four approaches are distinguished that could be used to explain cross-cultural variance in psychological functioning: (1) theoretical approaches such as the ecocultural framework (Berry, 1976; Georgas and Berry, 1995) and the cross-cultural domain framework (Poortinga, Kop and van de Vijver, 1990; van de Vijver and Poortinga, 1990); (2) studies that cluster many country-level indicators in order to arrive at a few broad dimensions (e.g., Georgas, van de Vijver and Berry, 2004; Ronen and Shenkar, 1985; Rummel, 1972); (3) frameworks that evolved from cross-cultural studies involving many countries (e.g., Hofstede, 1980, 2001; Schwartz, 1992, 1994); and (4) explanations of cultural differences in terms of artefacts or bias (van de Vijver and Leung, 1997, 2000).