Essence of fundamental rights – Article 52(1) of the Charter – Multi-level protection of fundamental rights in Europe – Sources of essence – European Court of Justice case law on ‘very substance’ of fundamental rights – Constitutional traditions common to the Member States – European Court of Human Rights – Court of Justice of the EU – Schrems – Principle of proportionality – Absolute theory – Relative theory – Classification of interferences with essence – Objective interference – Subjective interference – Absolute rights – EU methodology for determination of interference with essence