Redox-flow batteries (RFBs) are eminently suitable for the storage of wind and solar energy since their capacity and power capability are independently scalable. Furthermore, RFBs can be precisely adapted to the generator unit. However, common metal-based RFBs utilize toxic and high-price metal salts, hazardous and corrosive acidic electrolytes, and expensive ion-exchange membranes. By the use of redox-active organic molecules and polymers, whose solubility and electrochemical properties can be adjusted, as active materials, these limitations can be overcome. In this thesis, the synthesis and electrochemical properties of redox-active small molecules as well as polymer-based organic active materials for the usage in RFBs are studied. In this context, all-organic symmetric redox-flow batteries and zinc-organic hybrid-flow batteries are described. Moreover, an all-organic combined RFB, which uses a polymer and a small-molecule compound as charge-storage materials, is developed and the key factors in terms of its battery performance are investigated in detail.