The field of insurance fulfills many important functions. One of them is to provide policyholders and other persons entitled to compensation with a financial protection in the event of damage or other financial loss. At the same time, insurance companies accumulate enormous amounts of money, in the form of premiums paid, which they shall manage. According to the diversity of risks associated with an insurance business, the legislature has considered it necessary to limit the ability of insurance undertakings to take risks. One of these provisions – with such a purpose – is the prohibition of non-insurance activities. In other words, insurance undertakings are solely allowed to carry on insurance and related activities to the insurance business.  What is meant by permitted activities is not clear from a legal perspective. In the light of the sanctions that may be imposed on an insurance undertaking while carrying out an unallowed activity, it may be important to investigate the boundaries between permitted and unallowed activities. In the light of this, the thesis aims to examine (i) the distinction between permitted and unallowed activities and the motives behind the prohibition rule, (ii) how the prohibition rule relates to the specific risk regulation and the requirements of stability and prudent investments, and (iii) whether – in terms of the need for predictability, on the one hand, on the other hand, the need for principled regulation – there is a need to clarify the meaning of permitted activities.  The thesis describes FRL as a framework with its requirements for stability, prudence and a satisfying ratio of solvency and liquidity. According to the requirements imposed through FRL and the Solvency II regulation, the limits of permitted and unallowed activities, respectively, are examined.