Continuously increasing demands on product quality necessitate the application of an increasing number and variety of sensors in order to achieve stable and well-controlled production processes. While the basic function of a sensor is to acquire specific process-related information at the relevant stage of production and processing, hygienic application of a sensor will add additional demands concerning the sensors design and construction, its installation and integration into the process, as well as cleaning and maintenance issues. According to their working principles, all sensors rely on an interaction with the material to be processed. Therefore, the use of sensors is commonly associated with hygiene risks. In many cases, the basic measuring aspect of a sensor and the optimum hygienic design may conflict.This guideline is intended to advise both, sensor designers and manufacturers as well as those in charge of production machinery, plants and processes about the appropriate choice of sensors and the most suitable way for application in dry and wet processes.Sensors are crucial in the monitoring of the critical process steps as well as the CCP´s as established by the HACCP study of the process. Therefore validation and calibration of sensors in time sequences are essential. This guideline applies to all sensors coming into contact with liquids and other products to be processed hygienically. However, it focuses upon sensors for the most common process parameters, particularly temperature, pressure, conductivity, flow, level, pH value, dissolved oxygen concentration and optical systems like turbidity or colour measurements.The objective is to provide a guideline clearly describing standard hygienic requirements and recommendations for sensors and corresponding process adaptations.As for sensors, the more general recommendations on acceptable product-wetted materials, surface geometries, finishes and process fittings apply, this guideline will make wide use of references and citations from additional sources on related topics.