The evaluation of a surveillance system/component is the determination of its merit by confronting the results of the assessment with targets set by the stakeholders, standard criteria or a counterfactual system. The outcome of an evaluation is a judgement and/or recommendations placed in the overall surveillance context. An evaluation can be performed at any development stage of the surveillance system. Ideally, an evaluation is conducted in regular intervals in line with the policy cycle, by internal and/or external evaluators. One, several or all components in the surveillance system and any number of attributes and/or criteria can be considered, depending on the question and the context of the evaluation