Interpreting is a translational activity in which one produces a first and final target-language output on the basis of a one-time exposure to an expression in a source language. The most common two modes of interpreting are simultaneous interpreting, which is done at the time of the exposure to the source language, and consecutive interpreting, which is done at breaks to this exposure. Interpreting is an ancient human activity which predates the invention of writing. However, the origins of the profession of interpreting date back to less than a century ago.