The burden of proof has two interrelated aspects: material and formal aspect. Material aspect of the burden of proof allows to decide every civil trial – even that where the evaluation of the evidence left some doubts in the judge’s mind. The formal aspect of the burden of proof indicates the direction of the trial, especially when it comes to taking evidence. It is the party, not the judge, who bears the burden of producing evidence. It is also the party who has to persuade the trier of the fact of the truth of the alleged facts. But it is the institution of the burden of proof that allows the judge to decide every case. For that reason regulations governing the burden of proof are present in all proceedings. What is not commonly agreed is the answer to the question: does the issue of burden of proof belong to substantive law or is it a matter of litigation. The presented article tries to closer the arguments of both sides.