The final paper describes the topic of significance and importance of online reservations in hotel business. Online reservations are more and more prevalent in the hotel industry, and a large number of people decide on this type of reservation. In addition to being the simplest, it is possible to book a hotel on the other side of the world from the comfort of your own home. In addition to online reservations, the paper defines the very concept of hotel, hotel industry, as well as various forms of reservation IT systems. At the very beginning of the final paper, there is a definition of hotel and also the types of hotels according to services, where hotels are divided into top, medium and economy. After the division according to the quality of service, the paper also shows the division of hotels according to the number of accommodations, i.e. the number of people received. Through further chapters, the very concept of hotel management is defined, followed by an overview of the historical development of hotel management in the world, as well as in Croatia. In Croatia, the hotel industry began to develop in the most famous Croatian tourist town of Opatija, but the first registered hotel as such was opened on the island of Hvar. Further subchapters cover the types of hotels as well as their functions, followed by a new chapter. The penultimate chapter of the paper introduces us to the main important online reservation systems, which are explained in subsections called Time, Visibility, Easy collection and administration of data, Increase of income, Possibility of booking 24 hours a day and reservations via mobile phone, Less risk of double bookings, Less risk of losing data and Reviews. The last chapter of the paper is the conclusion, followed by the Bibliography and a list of illustrations.