The article refers to the impact of the Judgment of the General Court (of 10.09.2019 year) in the OPAL Case (T-883/16) on current and future energy policy of the European Union and its Member States. First of all it must be underlined that the present legislation and case-law did not explicitly define the concept of energy solidarity. In the legal doctrine, this term was mostly identified with the obligation of mutual assistance if, for example as a result of natural disasters, a Member State experiences a critical or emergency situation in gas supplies. That is why the judgement analyzed is crucial for proper understanding of the term of energy solidarity. In practice, it expands the concept of energy
solidarity and make it legal criterion. The court draws attention to at least two levels of understanding of the
above principle. Considering its position, the principle of energy solidarity not only concerns the interest of the
EU as the whole, but has to take into account the interests of individual Member States as well. In this respect, the commented decision is a milestone in understanding the principle of energy solidarity, its place in the legal system, and its application by the European Union and national authorities.