Silicon photonics has shown great promise as an integrated solution for efficient nonlinear optical interactions in compact, chip-scale devices. While there has been much work over the past decade on developing a variety of all-optical devices for telecom applications, an emerging area of research focuses on extending the operational wavelength of such devices to the mid-infrared (MIR) regime. By leveraging enhanced nonlinear optical effects and exploiting reduced losses at longer wavelengths, silicon photonic technology may be extended into a new realm of applications at MIR wavelengths. In this thesis we investigate nonlinear optical phenomena in silicon nanowaveguides for the MIR wavelength region. We present a numerical analysis of broadband four-wave mixing (FWM) and supercontinuum generation (SCG) in silicon nanowaveguides in the 2-[mu]m region. We demonstrate for the first time continuouswave FWM-based wavelength conversion between the telecom and MIR wavelength ranges. We also demonstrate the first silicon-based, octave-spanning supercontinuum (SCG) as well as the longest wavelength generated via SCG on a silicon chip. Next we numerically investigate silicon microresonator-based optical frequency combs using a modified Lugiato-Lefever model and discuss the implications of nonlinear loss effects, identifying regimes in the MIR in which broadband parametric oscillation may be achieved. While much of this work focuses on the silicon-on-insulator (SOI) platform and silicon dioxide or air claddings, we also introduce a novel waveguiding platform for wavelengths beyond 3 [mu]m. We design and fabricate devices using standard SOI wafers with a top cladding of silicon nitride and demonstrate broadband FWM near 2 [mu]m.