Ligand-responsive gene switches are cellular sensors that process specific signals into adjusted gene product responses and transform mammalian cells into useful cell-based machines for next-generation biotechnological and biomedical applications. In this talk, I will present how mammalian cells engineered with such gene switches can readily applied for biotechnological and diagnostic purposes. The construction of larger synthetic gene circuits, however, requires an additional gene control layer to connect multiple switches. RNA-based gene switches are perfectly suited for this function because they act on translation rather than transcription. In this talk, I will present how to build such RNA-based gene switches and implement them into large gene circuits with network topologies reminiscent to electronics that provide engineered cells the ability to perform complex information-processing tasks.