The aim of the article is to present theoretical research on international portfolio theory. The article describes the main research areas such as international efficient frontier, risk reduction through international diversification, the degree of risk reduction in different countries and sectors, and spread of international diversification into supra-regional level. The main objective is to present the impact of international diversification on portfolio risk based on the major international indices in the period of 2011–2015 with the use of expected rate of return and standard deviation. Portfolios from various regions of the world – Europe, the United States, and China – have been analysed. Empirical research has shown that the degree of risk reduction is connected with the level of international diversification. In the period of 2011–2015, the lowest risk characterized the S&P 500 portfolio, which in itself proved to be the most internationally diversified.

The aim of the article is to present theoretical research on international portfolio theory. The article describes the main research areas such as international efficient frontier, risk reduction through international diversification, the degree of risk reduction in different countries and sectors, and spread of international diversification into supra-regional level. The main objective is to present the impact of international diversification on portfolio risk based on the major international indices in the period of 2011–2015 with the use of expected rate of return and standard deviation. Portfolios from various regions of the world – Europe, the United States, and China – have been analysed. Empirical research has shown that the degree of risk reduction is connected with the level of international diversification. In the period of 2011–2015, the lowest risk characterized the S&P 500 portfolio, which in itself proved to be the most internationally diversified.