The use of Integrated Testing Strategies (ITS) in toxicological hazard identification and characterisation is becoming increasingly common as a method for enabling the integration of diverse types of toxicology data. At present, there are no existing procedures and guidelines for the construction and validation of ITS, so a joint EPAA WG5-ECVAM workshop was held with the following objectives: a) to investigate the role of ITS and the need for validation of ITS in the different industry sectors (pharmaceuticals, cosmetics, chemicals); b) to formulate a common definition of ITS applicable across different sectors; c) to explore how and when Three Rs methods are used within ITS; and d) to propose a validation rationale for ITS and for alternative methods that are foreseen to be used within ITS. The EPAA provided a platform for comparing experiences with ITS across different industry sectors. It became clear that every ITS has to be adapted to the product type, R&D stage, and regulatory context. However, common features of ITS were also identified, and this permitted the formulation of a general definition of ITS in a regulatory context. The definition served as a basis for discussing the needs, rationale and process of formal ITS validation. One of the main conclusions was that a formal validation should not be required, unless the strategy will serve as full replacement of an in vivo study used for regulatory purposes. Finally, several challenges and bottlenecks to the ITS validation were identified, and it was agreed that a roadmap on how to address these barriers would be established by the EPAA partners.