The structural properties of the polysilicon-to-silicon interface affect the electrical characteristics of devices with polysilicon contacts. The current characteristics of advanced bipolar transistors with polysilicon base and emitter contacts are very sensitive to the presence of interfacial oxides and segregated dopants. Hence, bipolar transistors provide an excellent tool for studying the effects of different interfaces on minority carrier transport. The transport of majority carriers through polysilicon-to-silicon interfaces is best investigated with contact resistance structures. In this paper, we review the correlation between interface morphology and the electrical properties of a variety of interfacial layers, ranging from native oxides to chemical oxides or thermal nitrides. Measurements on both npn transistors and contact resistance structures provide quantitative information on the trade-off between base current (i.e. current gain) and emitter resistance. Within this constraint, a variety of electrical characteristics can be obtained by tayloring the nature of the polysilicon-to-silicon interface to the device application of interest.