Electronics applications such as light emitting devices for lighting and flat panel displays, transistors, solar cells and sensors based on p-conjugated organic materials are presently being developed and have in some cases reached the market. Here is given an overview of the materials properties of p-conjugated molecules, in particular how optical absorption and luminescence as well as the electron- and hole-injection levels can be tailored through organic synthesis. We briefly discuss the strengths and weaknesses of organic electronic and spintronic applications where p-conjugated materials currently are used. The importance of interfaces in organic electronic applications is highlighted as e.g. solar cells, light-emitting diodes and field-effect transistors are multi-layered devices where their ultimate performance is to a large extent dominated by the electronic processes at interfaces. The relative position of energy levels across a stack of thin organic layers is important for charge injection/separation and hence for device engineering and optimization. For organic photovoltaic devices, the donor-acceptor interaction is of particular importance as it strongly effects not only the efficiency exciton dissociation and charge separation but also the size of the open circuit voltage. We discuss how the behavior of specific organic heterojunctions can be predicted by the Integer Charge Transfer (ICT) model [1-3] using values of the integer charge transfer states (EICT+, E ICT-) as measured by ultraviolet photoelectron spectroscopy (UPS).