The article presents the question of solidarity in relation to the energy policy of the European Union. This topic seems particularly important in the context of the crisis of the European integration process, which includes, in particular, economic problems, the migration crisis and the withdrawal of the United Kingdom from the European Union (Brexit). The issue of solidarity was analyzed from the legal and formal, institutional, and functional and relational points of view. The aim of the article is to show to what extent the theoretical assumptions, resulting from the provisions of European law on the solidarity, correspond with the actions of the Member States in the energy sector. The practice of the integration process indicates that the particular national economic interests in the energy sector are more important for the Member States than working towards European solidarity. Meanwhile, without a sense of responsibility for the pan-European interest, it is not possible to effectively implement the EU’s energy policy. The European Commission – as the guardian of the treaties – confronts the Member States with ambitious challenges to be undertaken “in the spirit of solidarity”. In the verbal sphere, this is supported by by capitals of the individual countries, but in practice, the actions taken divide the Member States into opposing camps instead of building a sense of the European energy community. This applies in particular to such issues as: the management of the energy union, investments in the gas sector (e.g. Nord Stream I and Nord Stream II), and the position towards third countries – suppliers of energy raw materials to the EU (in particular towards the Russian Federation). Different views on the above problems make it extremely difficult for Member States to take action “in the spirit of energy solidarity”. Thus, the energy problem becomes another reason for the weakening of European unity.