In recent years, the sector of information and communication technology represents a driving force of domestic economy. At the same time, this sector is characterized by fast and dynamic changes which in the demanding business environment require an immediate and adequate response. Information and communication technology today is a global activity for which competition is of key importance, on the domestic, as well as the global market. Therefore, it is important that the ICT sector organizations respond fast to changes, thus ensuring their competitive position in order to achieve profit growth. That makes change management highly significant for the competitiveness of the ICT sector and simultaneously represents one of the greatest challenges of modern business. The sample of research structured by data gathered from 103 employees in the domestic ICT sector offers enough elements to establish a quality methodological framework for synthesis in monitoring of the influence of change management on competitiveness in this sector. The research results undeniably point to the conclusion that change management is of key importance for establishing and maintaining a competitive position on the market. The total reactive relation of change management to competitiveness shapes the model of change management by transferring its positive outcomes to the sector, and by that the economy as a whole. This doctoral dissertation has offered evidence on the possibility of using the ADKAR model of change management in the analysis of the need for changes, implementation and monitoring of the course of changes in the organizations of the ICT sector, and has confirmed the influence of change management on competitiveness. In order to produce conclusions which confirm the hypotheses set in the introductory part of the doctoral dissertation, this dissertation has encompassed the theoretical framework of change management with emphasis on the most used models of change management, demonstration of the economic position of the ICT sector in the economic structure of the Republic of Croatia, determinants of change management in the ICT sector which relate to the ADKAR model of change management, determinants of competitiveness of the ICT sector, and an empirical research has been conducted, which has confirmed that change management by applying the ADKAR model in the Croatian ICT sector can ensure a competitive position of the organization, and as such the economic growth and development of economy as a whole.