Despite the importance of the co-evolution approach in various branches of research, such as strategy, organisation theory, complexity, population ecology, technology and innovation (Lewin et al., 1999; March, 1991), co-evolution has been relatively neglected in international business and ethics research (Madhok and Phene, 2001). The purpose of this article is to show how co-evolution theory provides a theoretical framework within which some issues of ethics research are addressed. Our analysis is in the context of the contrasts between business systems (North, 1990), and in particular the distinction between informal systems and those systems where institutions are formalised in law. This complements the growing research on comparative corporate governance and capitalisms (Chandler and Hikino, 1990; Choi et al., 1999; Whitley, 1994). The synthesis of co-evolution and analysis of divergent institutional environments in ethics research can also complement the globalisation and MNE approaches to international business research.