The main purpose of this doctoral thesis is to theoretically and empirically examine the value of loyal guests and methods of maintaining their loyalty using the GRM (Guest Relationship Management) tool – loyalty program. Main goals arise out of a defined main purpose. This study aims to: a) prove that hotel groups (hotel brands) are more successful in managing guest satisfaction by using loyalty programs when compared to domestic hotel groups and unaffiliated hotels in Croatia, b) indicate main disadvantages of the implementation of GRM tools and improvement possibilities in managing key guests’ satisfaction, c) analyze current views and opinions on loyalty programs from the perspective of hoteliers, d) determine the quality of information available to guests in terms of quality, quantity and value in time. The most important scientific contributions in this doctoral dissertation are: a) thoroughly defined loyalty program standards (according to the key components of information communication technology – ICT), which can also be used as a form of valorization of already existing hotel loyalty programs, b) conducted empirical study on a sample of 189 hotels. Descriptive analysis, t-test and analysis of variance were performed using the SPSS statistical package, in order to test the proposed hypothesis and to accomplish defined objectives, c) loyalty program model, which shows a data flow in conditions of guest arriving with and without a loyalty program. The results of the study indicate: a) causal relationship of GRM system levels and data usability (the higher the GRM system level, the higher the usability of data and efficiency in data managing), b) substantial difference in the quality of using loyalty programs among international hotel groups and domestic hotel groups, c) extreme incoherence within small hotels and their insufficient level of the GRM system, d) proportional relationship of the application and effectiveness range of a loyalty program (the wider possibility of application, the higher effectiveness of loyalty program). The study has several limitations: relatively small number of hotels with an implemented loyalty program, short and specific time period during which the research was conducted, representative sample of hotels, organizational structure complexity of the hotel groups in Croatia (unimplemented loyalty program in all of the hotels within one hotel group).