Over the past decade HTS thin-film technology has matured to such a degree as to allow the beneficial implementation of I-ITS components into operational systems. This chapter is concerned with the application of low conductor losses in epitaxial FITS thin-films to passive RF components. Following a phenomenological introduction to the RF current transport properties of superconductors, application aspects are discussed in three steps. First, realization and properties of HTS components, like resonators, filters, delay lines and antennas are outlined. Next, the impact of superior HTS component performance is investigated on the subsystem level, covering receiver front-ends, wideband cueing receivers and stable oscillators. Finally, the pay-off of an implementation of HTS technology is discussed for two representative system applications, namely communication satellites and terrestrial mobile communication systems.