Food safety is now seen to be managed and controlled by three fundamental requirements. HACCP programmes control hazards associated with the process, processing environmental prerequisites control hazards associated with the processing environment, and quality systems (e.g. ISO 9000) manage quality-related prerequisites, e.g. supplier approval and control, control of non-conforming products, customer complaints, traceability and recall, etc. This chapter focuses on processing environmental prerequisites and covers the design of the food manufacturing infrastructure (the factory, the process lines and services, the equipment and the food operatives) and the hygienic practices to keep the infrastructure in optimum condition (maintenance, pest control, cleaning and disinfection and personal hygiene). The management of environmental prerequisites initially involves ensuring that all generic prerequisites (such as cleaning and disinfection) are undertaken to best practice and appropriately validated. Further to this, any remaining sources of environmental hazards, and the transfer vectors by which they can contaminate food products, are assessed and appropriate controls installed. If controls are identified such that any failings in these controls would most likely result in product contamination, such controls are termed operational prerequisites (OPs). OPs are managed in a similar way to HACCP critical control points (CCPs) so that in the same way as CCPs are the major focus of attention in the control of the food process, OPs are the major focus in the control of the processing environment.