Renewable energy sources are alternative energy sources that can never be depleted, but are constantly renewed. These are natural energy sources, the most famous being solar energy, wind, water, tides, biomass energy and geothermal energy. Renewable energy sources are key in the fight against climate change. The development of new technologies leads to the development of renewable energy sources. Today, all attention is focused on renewable energy sources, making these forms of energy one of the primary interests of almost every state and its policies. The energy development strategy of the Republic of Croatia is based on the balance between constant energy supply and other requirements related to economic and environmental policy. The regions of Slavonia and Baranja have great potential for the development of renewable energy sources, especially biomass. In the last ten years, several biogas and biomass power plants and photovoltaic power plants have been built in this region, and the construction of new facilities is also planned. For the proper valorization of agricultural biomass, it is necessary to invest much more work and financial investments in the development of this and other forms of renewable energy sources. The paper introduces the forms of RES and their main properties and classification, compares the situation in the world, the European Union and Croatia, and the legislation of the Republic of Croatia relevant to the field of RES. The potentials of using the most potent forms of RES in Slavonia and Baranja are described in detail, as well as examples of capacities for the use of RES in that area. In conclusion, the most important steps that should be taken to accelerate the use of RES in Croatia, and especially in Slavonia and Baranja, are highlighted.