The doctoral thesis, on the basis of the elements for the assessment of the necessity of restricting the freedom of expression of website operators in a democratic society, formulated in the cases Delfi AS v. Estonia, MTE & Index v. Hungary, Pihl v. Sweden and Tamiz v. the United Kingdom, investigated by the European Court of Human Rights, established and assessed the criteria justifying the application of website operators’ non-contractual civil liability in case of violation of the right to privacy of third parties by anonymous comments. The first part of the work, which is based on the concept of structuralism, reveals the content of freedom of expression of website operators arising out of Article 10 of the ECHR and of the category of private life, which is an assumption for restricting the freedom of expression of website operators, as well as distinguishes the specific criteria justifying the application of website operators’ civil liability in case of violation of the right to privacy of third parties by anonymous comments. The second part of the doctoral thesis, which is based on the principle of functionalism, using the complex analysis of the judgements made in the above-mentioned cases of the European Court of the Human Rights, evaluated the content of each criterion, compared the peculiarities of their content and application in different cases, discussed the problems and significance of these criteria, and determined their interrelation. This is the first scientific research of this kind not only in the context of Lithuanian, but also of the European tort law. The research has shown that the key criteria justifying the application of website operators’ civil liability in case of violation of the right to privacy of third parties by anonymous comments are the following: (i) the context in which the comments are posted and the content of the comments themselves and (ii) prior measures taken by the website operator to ensure the legality of the comments and actual behaviour after the comments were posted. Meanwhile, other criteria distinguished by the case-law of the European Court of Human Rights (i.e. (i) the actions of the victim before and after the occurrence of comments, (ii) the consequences of the comments on the victim, (iii) the possibility of civil liability of the authors of comments as a certain alternative to the liability of the website operators, and (iv) the consequences of civil liability for the particular website operator) are to be considered as additional and having no essential impact on the fact of the application of website operators’ civil liability, yet significant when making a decision on the extent of the application of website operators’ civil liability.