Institutional investors, including in particular pension funds, play a significant role in financing both listed and unlisted companies and, once invested, frequently act as active investors. The purpose of this article is to describe and analyse the regulation based on the so-called “prudent person principle” which determines how pension funds invest and subsequently manage their investments. The prudent person principle is EU-based. The Danish implementation has primarily taken place in the preparatory work for the relevant Danish acts. This creates ambiguity about the content and scope of the rules. In their oversight the Danish FSA have taken the view that investments in alternative assets possess the highest risk and have issued guidelines relating to such investments. However, in relation to most of the pension funds’ investments, which are made to obtain exposure to the listed markets, the Danish regulation remain silent. The analysis set out in the article includes the requirements which follow from the prudent person principle in relation to both listed and unlisted instruments as well as the considerations that should be made when investing in derivatives.