The main purpose of this thesis was aimed at making a contribution to the valuation of the importance of intellectual capital in the company's operations. The main goal of the research was to examine the impact of intangible assets, human, structural and relational capital on the efficiency, profitability and market valuation of Croatian companies. The theoretical part of the thesis discussed the concept, significance and components of intellectual capital, including the presentation of accounting aspects of recognizing, measuring and presenting intangible resources and considering the possibilities of using monetary methods of intellectual capital valuation. In the empirical part of the thesis, an econometric analysis was performed on a planned sample composed of companies whose shares are traded on the Zagreb Stock Exchange for the period from 2009 to 2019, followed by the expanded sample composed of large companies in the Republic of Croatia for the period from 2017 to 2021.The validity of the set hypotheses was tested by conducting descriptive statistics, correlation and panel analysis. The results of the hypothesis testing show the greatest impact of intellectual capital on the profitability of the company measured by the rate of return on investments, partially on the efficiency measured by the turnover of assets, whereas the influence on the ratio of the market to book value of the company was not confirmed by this research. The main limitation of the research is related to the limitations of the existing accounting system, which does not enable the application of more direct measures of the relationship between the components of intellectual capital and the financial performance of companies. This thesis, in the theoretical and empirical part, represents a contribution to the research of the impact of intellectual capital on the business performance of companies. The model proposed by this research differs from the existing ones by introducing two new components of intellectual capital (recorded intangible assets and relational capital), which makes the analysis more theoretically grounded, and at the same time enables a more comprehensive overview of its impacts. The conducted empirical research is the first extensive research into the effects of intellectual capital on the performance of Croatian companies. In addition to contributing to the scientific literature, the conducted research can be useful to economic policy makers, experts focused on improving business information, and on a practical level, to investors, managers and a wider business community when making business decisions and evaluating business efficiency.