Since the discovery of conductivity within doped polyacetylene polymers [1] and organic crystals [2] , the field of organic electronics has been growing extremely rapidly. The development of new applications is largely based on the ability of chemists to synthesize new molecules to create stable materials with different physicochemical properties, since the organic materials have to satisfy a large number of technical requirements to be incorporated into a device. The properties of organic materials can be tuned in several ways. One attractive method consists of the incorporation of heteroatoms and heterocycles into π-conjugated systems. Indeed, heterocycles like thiophene, pyrrole, and their derivatives are now widely used to modify chemical and physical properties of -conjugated systems. It is interesting to note that the incorporation of organophosphorus derivatives into devices has been achieved only recently, despite decades of research on such species. In this chapter, we will highlight the different kinds of organophosphorus-based materials that have been used in electronic devices, [3] such as organic light-emitting diodes (OLEDs), organic photovoltaic cells (OPV cells), dye-sensitized solar cells (DSSCs), organic field-effect transistors (OFETs), resistive memory devices, batteries and electrochromic cells. Although there are numerous other interesting and promising organophosphorus materials, many of them have not yet been incorporated into electronic devices. [4] Only five types of organophosphorus building blocks have made it to the finish line; they are triaryl phosphines, phosphetes, diphosphacyclobutanes, phospholes, and cyclophosphazenes (Figure 1). Figure 1. Organophosphorus materials used in optoelectronic devices. Phosphines Aryl phosphines are the most extensively researched group of organophosphorus materials due to their widespread use as ligands in transition metal catalysis. It has been demonstrated that the lone pair on phosphorus is only slightly involved in the delocalization within a conjugated system [5] due to phosphorus' tetrahedral shape and high inversion barrier (30-35 kcal mol-1).