The aim of the study was to determine the most effective model of legal regulation of the form of declaration of will in legal transactions from the survey of the legislation of several countries and their respective jurisprudence. The research covered the methods of statistical analysis, comparative law, dialectics and legal epistemology, as well as data selection and legal modeling. It is shown that the model of legal regulation of the form of declaration of will, which is based on the principle of free choice of the form of declaration of will, is the most effective in terms of these indicators in the case of: (Greece, Poland, Czech Republic). At the same time, these States provide for strict requirements for challenging legal transactions and provide for the prohibition of abuse of rights. It is concluded that it is justified that in the majority of states the principle of valid will is applied when concluding legal transactions. Moreover, the results of this study can be used to develop proposals for the improvement of legislation in the field of regulation of the forms of declaration of will in the conclusion of legal transactions in their various forms and modalities.