Objective - In line with the One Health concept, international organizations and the scientific community are strongly supporting the implementation of multisectoral surveillance systems to improve the management of health hazards at the human-animal-environment interface. Such surveillance systems call for the establishment of collaboration across sectors and disciplines that must be evaluated to ensure they are appropriate and functional to produce the expected results. In this context, we aimed to developed a tool, ECoSur (Evaluation of Collaboration for Surveillance), to evaluate collaboration taking place in a multisectoral surveillance system. Materials and Methods - Based on core collaborative characteristics for the governance and operation of surveillance activities and attributes used in existing evaluation framework for surveillance and One Health initiatives, we have developed a list of attributes and indexes to evaluate the organisation and functioning (at both governance and operational levels) and functions of collaboration in a multisectoral surveillance system. Results - The developed tool consists of an evaluation matrix (one spreadsheet), documents to collect necessary data to conduct the evaluation (one spreadsheet and one text document) and a guidance for potential users. Evaluation results are automatically generated and displayed in graphical representations. The tool was effectively applied to surveillance of different type of health hazards (antimicrobial resistance, foodborne pathogens and zoonotic diseases) and in different surveillance contexts (well-established surveillance systems and in-development ones), both in developed and developing countries. Conclusion - ECoSur is the first evaluation that allows an in-depth evaluation of collaboration between surveillance programmes in line with the One Health context. The tools has provided evidence of its applicability and adaptability, as well as its capacity to engage surveillance actors in