Publisher Summary In the past few years, SiGe alloys have become an important alternative to pure silicon for high performance integrated circuits (ICs) and devices. This chapter on the whole gives a striking account of SiGe alloys, focusing on their properties, design, fabrication and applications. The advantages that SiGe alloys provide for circuits and devices arise from its different physical properties as compared to pure Si. The composition dependence of the bandgap and band offset energies can produce heterostructures similar to those of the group III-V compound semiconductors. The Si1-xGex alloys form a solid solution that is miscible over the entire range of Ge atomic fractions x. The addition of Ge to Si decreases the optical bandgap for absorption at longer wavelengths, depending on composition and layer strain. The band offsets in heterojunctions of SiGe with Si can be controlled in both positive and negative energy directions using composition and strain. Predicting the details of device behavior by modeling and simulation is performed by applying the carrier transport equations of drift, diffusion and recombination, along with Poisson and Schroedinger equation solvers. Computer aided techniques have revolutionized the device and circuit simulations. The chapter also describes the main epitaxial techniques for growing SiGe thin films such as chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and ion implantation. Furthermore it provides details of SiGe device characteristics and limitations, theory and models, performance, sensitive parameters, design trade-offs, frequency response, noise properties, comparisons with alternative structures, and applications. Finally the chapter illustrates various parameters that could be used to characterize SiGe devices, such as direct current and low-frequency electrical measurement, microwave measurements, electrical noise measurements and optical measurements.