The scale–up from bench-top bioreactors to larger, pilot systems can seem daunting. The list of user requirements specifications is much longer, and the manufacturer will provide a peculiar drawing called a P&ID. Reading these is second nature to a Bioprocess Engineer. For someone without such a background, this may be a strange concept. Nevertheless, with a bioreactor in the centre of your process, it is vital to link bioprocess technology and mechanical engineering in a schematic representation. This article shows you how to interpret your P&ID and to understand the functionalities of your bioreactor and its capabilities.