The EFSA asked the Panel on Animal Health and Welfare to develop a guidance document on good practice in conducting scientific assessments in animal health using modelling. In previous opinions, the AHAW Panel has responded to two-thirds of animal health-related mandates using some kind of modelling. These models range from simple to complex, employing a combination of scientific, economic, socio-economic or other types of data. Hence, there is strong interest in the development of a guidance document to integrate modelling efforts into the routine process of EFSA working groups. In this document, an ?operating procedure' (OP) for the use of modelling within an AH working group is presented. The OP provides a detailed flowchart enabling modelling to be transparently and consistently integrated in the assessment. The OP is structured into phases. These phases combine the relevant standard operating procedures and working instructions of EFSA with the modelling process. Each phase includes roles and actions to be taken, expected output and the sequence of agreements that need to be made between all partners in the scientific assessment. In conclusion, it is expected that adherence to the OP will improve transparency of models in EFSA outputs, and it is recommended to adopt it as a standard procedure when responding to AHAW mandates.