Tour operators' play a major role in the development of tourism because they have the power to create demand for a specific tourist offer. They also have well-organized distribution channels and invest enormous efforts and funds to promote the tourist destination. Tour operators' save tourists money and time and undertake the obligation to fulfill all the expectations of tourists. Their main source of income is the sale of their own products or package holidays on the market. The subject of the paper is the role of digital marketing in the tour operators' business based on promoting package-holidays. The main goal of this work is to explain the concept of tour operator, what types of tour operators exist on the tourist market and the presentation of their business on the market. The goal is also to explain what types of digital marketing the tour operators' uses in the daily promotion of the package holidays and what role digital marketing plays in promoting the tour operator package holidays on the market. In the "TUI" case study, the topic is about main characteristics on the market and the services it offers, as well as traffic from digital services and examples of promotion through mobile applications, are listed.