The participation of courts in law making has undoubtedly been happening for many years already; in the Czech Republic, we started to talk about the issue relatively recently, it was first explicitly mentioned in the academic literature mostly reflecting the impact of German authors, at the beginning of this century. The starting point of this article is the fact, that courts participate in law making when the law is applied against the clear diction of the law, when courts find in the legal texts one of many possible loopholes. The fact is that courts can reveal relatively arbitrarily another ones, and furthermore, courts often participate in law making without pronouncing any loophole expressively, namely under a situation, where the text of the regulation is entirely clear and indisputable. As it can be seen from the examples mentioned above, the boundaries or limits of such activity of courts complete are shifted permanently and increasingly and when such activity is undertaken by the supreme judicial authority or by the Constitutional Court, there can be found no means for remedy. There is no doubt, that the above mentioned tendency has become reality, however, there is no doubt, that courts should abide rather by the principle of self-restraint, otherwise, one of the main principle of the legal state will be threatened permanently, and that is legal certainty.