Organic photodiodes (OPDs) are a new category of photodetecting devices that would be well suited for large-area electronic products on flexible substrates. Researches and developments in this field cover a large spectrum of scientific and technological domains such as chemistry of materials, physics of interfaces, physical chemistry of materials blends, electronic processes in organic semi-conductors, inks formulations and printing technologies. Even if organic photodetectors could rely on the recent achievements made in the field of organic photovoltaic (OPV), they have their own technical requirements and performances specifications. This paper gives an overview of the important aspects related to OPD.