This paper focuses on the topic "Comparative analysis of the application of telemarketing as a promotional tool in B2B and B2C businesses on the European market." The paper explores the main differences in the application of telemarketing as a promotional tool in companies operating on the B2B and B2C markets. The main goal of the paper is to provide a better insight into telemarketing as a promotional tool, showing its advantages and disadvantages, as well as the differences in the respective application depending on the type of business in which it is used. In the theoretical part of the paper, promotion and direct marketing, of which telemarketing is one of the main tools, are briefly described, as well as the origin and development of telemarketing. Furthermore, the differences between B2B and B2C markets are presented, examples of good practice of using telemarketing as a promotional tool in both types of business are given, and trends on the global and European market are presented. Employing the approach of in-depth interviews with marketing experts, the empirical research gathers opinions and answers about the application of telemarketing as a promotional tool in the daily operations of certain companies operating on the B2B and B2C markets. Attitudes and opinions on the possibilities of improving the application of telemarketing are collected, as well as views on the future of telemarketing as a promotional tool in both types of business. Based on the research results, conclusions and recommendations for practice in the future application of telemarketing as a promotional tool are made.