Book excerpt: Want an overview of where the technology of terahertz detection has been going? Here it is. The technology has largely been developed around expensive and bulky femtosecond laser systems but, as described in this book, advances in semiconductor superlattice technology are leading to compact "electronic" sources such as the quantum cascade laser, two-terminal "Gunn" type oscillators and even a THz frequency amplifier. These advances towards electronic (as opposed to optical) THz systems mean that the technology will become portable and much less costly.