In recent years, a fast development on terahertz science and technology has been achieved. Various terahertz waveguides and waveguide-based devices have been created. These waveguide devices include metal waveguides, photonic crystal waveguides, photonic crystal fibers, polymer waveguides, plastic waveguides, and sapphire fibers, etc. Therefore, an overview on terahertz waveguide-based devices has been presented in detail.