This “real-time” form of interpreting requires highly specialised training, because the interpreter must provide the translation of what is being said almost by speaking “on top” of the person speaking the source language: hence the term “simultaneous”. In simultaneous interpreting, two interpreters work together in a booth for a maximum of seven hours in total, taking it in turns so as to maintain concentration constantly at the required level. Instead of a booth, a portable briefcase-like device equipped with a microphone and earphones may be used, especially for situations in which both the interpreter and the listeners have to move from one place to another.

The number of interpreters required and the fees charged may vary depending on the languages the meeting is conducted in, the working hours and the subject dealt with. A single interpreter per booth may only be used for services lasting no longer than an hour.