The topic of this paper is to provide insight into the content of corporate income tax and issues related to tax reliefs and incentives that can be achieved in the system. Corporate income tax is the part of the tax system of the Republic of Croatia and represents the revenue of the state budget. It belongs to a group of state taxes. The aim is to facilitate the review of the opportunities that entrepreneurs can use when calculating the corporate income tax returns. Tax reliefs and incentives that can be achieved in the system are classified into several categories. The Republic of Croatia with the rate of corporate income tax of 20% belongs to the group of countries that are below the European Union average, but when compared to the neighbouring countries, corporate income tax is the highest in the region. Reduction of the tax rate is one of the forms of regional development stimulation, which can be achieved in areas classified according to a certain criteria. In the territory of the Republic of Croatia it is possible to achieve the reduction in corporate income tax on the basis of investments for entrepreneurs classified into specific groups according to entrepreneur size criteria. Corporate income tax rates reduction is achieved in a specific period based on a specific amount of investments and the number of jobs created. The tax base reduction can be achieved by accelerated amortization of fixed assets according to prescribed criteria. Reinvestment is one of the possibilities which enable the entrepreneur tax base reduction for the profit they decide to leave in the company and invest in fixed assets, increasing the share capital of the company, which is one of the conditions. It is possible to reduce the tax base for the costs of education and training of employees and for research and development costs. In the end of the paper the final considerations for the overall theme of the work are given.