As of the beginning of 2016 the principle of resolving possible interpretation doubts for the benefit of a taxpayer (in dubio pro tributario) was introduced to the Polish legal order. This rule was upgraded to the tax law principle expressed directly in Art. 2a of the Act of 27 August 1997 – Tax Ordinance. Such a decision of the legislator resulted from a prior referendum, wherein nearly 95% of voters supported the introduction of this principle, perceiving it, apparently, as an instrument that would enhance the practice of tax law application by tax authorities. After several years, it can be assumed that these hopes have not been fulfilled since this principle has not been applied more widely in the practice so far. The purpose of this study is to present both the very essence of in dubio pro tributario principle and experiences concerning its application in recent years, with a particular focus on the rulings issued thereon by administrative courts and Constitutional Tribunal.