The work consists in an in-depth study of Article 26 eIDAS Regulation, which governs the requirements for advanced electronic signatures. The work analyses the general principles set out in this provision, namely: a) the principle of technological neutrality; b) the requirement of the unique link to a signatory and the capability of identifying a signatory; c) the requirement of the sole control of the data by which a signature is created; d) the requirement of the detectability of any subsequent change in the data.