"In the obviously increasing need for quality control in building, a renewed attention for the concept of function may be observed. Although the history of "function goes back as far as Vitruvius, a considerable amount of confusion about this concept seems to exist, disturbing communication and hampering decision-making, especially in the promising surroundings of interdisciplinary cooperation. It turns out that the basic mathematical concept of function is surprisingly well applicable on architectural design. The use of the mathematical way of thinking about "function" also enables to relate conceptually experimental research and design activities. Some simple examples orginating from both fields will be elaborated."