A survey of the most common silicon-on-insulator (SOI) substrates and waveguide structures, as well as an evaluation of their applicability in optical telecommunication at the 1550 nm wavelength is presented. The design, fabrication and characterization of straight and bent SOI waveguides, as well as a thermo-optical SOI switch are described. The propagation loss of the realized SOI waveguides is below 0.25 dB/cm and thermo-optical switching is demonstrated at 10 kHz. The effect of cladding material on top SOI ridge waveguides on the polarization properties of straight and bent waveguides, as well as on directional couplers, is discussed. Both polarization independent and polarization maintaining waveguides are demonstrated. Finally, a basic principle of multi-step SOI waveguides is proposed. As examples of the potential in multi-step processing, efficient coupling between different rectangular, ridge and photonic crystal waveguides, ultra-small bends, waveguide mirrors, and extremely short multi-mode interference couplers are described.