Tour operators represent partnerships in the tourism market that, through their integrations, contribute to the increase of the total world tourist traffic, thus creating a large number of highly concentrated tourist companies at the world level, which conclude contracts for the sale of tourist arrangements to tourists. In this way, they create a megatrend of the modern tourism market, however, their partnerships must be based on the legal bases and regulations issued by the countries in whose markets they operate. By mediating between tourists and their departure to the desired destination, they realize their basic function - mediation between tourists and the destination and bringing them to the desired place, thus contributing to the overall realization of their tourist needs. The research compares the sustainable practices of two intermediaries, TUI as the world's most famous tour operator, and UNILINE as the most famous Croatian tour operator. In the final part of the paper, recommendations for the future business of tour operators are given, as well as examples for market maintenance.