Principally, an index is a composition of equities which meet defined criteria. The best-known are the DAX, the Nikkei Index and the Dow Jones Index. The indices differ in the different composition of the portfolios. The portfolios might consist of equities of blue chips or of small and medium companies, of european or american equities etc.. Index families consist of more than one index with different portfolio managed by the same index provider.

In the last years some index came up that select the companies by sustainable criteria. As well as the funds, they use excluding and positive criteria for the selection of companies. A special approach is the best-in-class approach which means the selection of the best companies of a sector.

Indexes have the important function to help the investor to estimate the success of the own investment (in companies to the index). However, some SRI-Index-Funds have been developed. An index fund reflect the composition of an index completely or almost completely. The investment success should be similar to the development of the index. This is called passive fund management