The purpose of this master’s thesis is to investigate to what extent ESG assets and traditional benchmarks affect one another. Since sustainable investment is a growing segment of the financial market, investors need to be informed about how it may affect their portfolios, and by extension if it can be used for portfolio diversification. By using an AR(1)-GARCH(p,q) model and a Diebold-Yilmaz spillover approach, we can measure the spillover effects between ESG indices and other benchmark indices for both return and volatility. We find that country-level ESG indices are more integrated with other country-level ESG indices than other assets, and that country-level ESG indices transmit more to the MSCI world ESG index, MSCI world equity index, Crude oil, Gold, and our currency index EUR/USD. These findings hold true for both return and volatility spillover. Thus, our policy implications are that including country-level ESG assets in the portfolio can decrease portfolio risk and help minimize the contagious effects of shocks on the portfolio.