In recent decades, the scientific community has increased its interest in research into the effective tax burden. In the context of the above, a special segment is occupied by studies of determinants that affect the effective tax burden of companies, and these studies are still in the phase of research growth. Therefore, the primary goal of the doctoral thesis is to identify the determinants that affect the effective tax burden of companies in the field of information and communications activities in the Republic of Croatia. The research is longitudinal, because the time horizon primarily covers the period from 2008 to 2016. In the analysis, for which data were obtained from secondary sources (the database of the Financial Agency and the State Statistical Office), panel regression analysis methods were applied. The findings of the research show that information and communication activities are predominantly labor-intensive. Determinants have been identified that have a linear impact on the effective tax burden of companies from the analyzed activity, namely: effective tax burden from the previous period, size, indebtedness, capital intensity, inventory intensity, labor intensity and real GDP growth rate. The identified determinants differ depending on sub-samples of company size, activities, or divisions of the area and location of the company. Also, the non-linear influence of the variables of size, indebtedness and capital intensity on the effective tax burden of the company was identified, and these also differ depending on the sub-samples of the department of activity, size and location of the company.