The interrelationship between international stock markets is a key issue in international portfolio management and risk measurement. The dynamics of security returns and their risk characteristics have a crucial role in the financial market theory. Recent empirical studies have tested market efficiency measuring the degree of integration of international financial markets. These studies have shown that international markets react quickly to news but they are volatile and difficult to predict, with a changing correlation structure of security returns among countries. In this paper the nature of the relationship between the major international stock markets in Canada, Japan, UK and the US, is analysed using the common trends and common cycles approach. The presence of co-movements is investigated to try to detect a long-term stationary component, the common trend, and a short-term stationary cyclical component, among international stock markets. The implications for international portfolio management are also discussed.Common cycles, common trends, cointegration, VECM, market diversification,