Microelectronics based on semi-conductors plays an important role in information technology since several decades. However, for the high rates needed for todays highly performing systems of telecommunications, the new optoelectronic technologies use processes involving the photon as well as the electron. Thus, what is usually called "Molecular Optoelectronics" has been developed since over the last ten years: it requires the expertise of both physicists and chemists. This molecular approach of information technology is based on a deep knowledge at the molecular level, from which are built complex supramolecular assemblies having specific physical properties. This area of investigation is nearly infinite since the choice of molecules able to supply the elementary bricks of the assemblies is unlimited, It has also to take into account the establishment of strong correlations between the structure and the optoelectronic properties of the supramolecular assemblies. Due to the large possibilities of molecular engineering, organic materials are very promising for many optoelectronic applications. In this chapter we will describe three of them. The first one deals with fullerene derivatives which can be used in photovoltaic cells. The second one concerns photorefractive polymers for recording and storage of optical informations in holograms. Finally, the third one concerns electroluminescent conjugated oligomers and polymers used in large flat displays. In connection with the latter, the way to prepare and to control the quality of thin films obtained by the Langmuir-Blodgett technique will be described.