The close interactions between humans, animals, and the environment, can lead to the emergence of infectious diseases through spillover events. Early warning surveillance systems at the human-animal-environment interface are pivotal to enable timely public health actions. Work Package 4 (WP4) of UNITED4Surveillance aims to establish and strengthen partnerships in a One Health approach, emphasizing structured data sharing for effective public health surveillance. This is achieved by supporting European Union Member States and Join Action partner countries in developing One Health surveillance structures at the national level that integrate data from human, animal, and environmental domains. This integration is intended to enhance the capability of detecting emerging pathogens, identifying outbreak sources, and conducting research for targeted interventions. WP4 is organized around three disease groups: foodborne diseases, zoonotic influenza, and vector-borne diseases. The tasks within each group encompassed three subtasks: 1) goal definition and stakeholder analysis, 2) systems mapping of the current and desired situation, and 3) piloting promising approaches. The first two subtasks were executed collaboratively across disease groups to ensure a consistent methodology. Countries aimed to align on specific pathogens within each disease group for shared experiences. In the initial subtask included stakeholder analysis, utilizing Mendelow’s matrix, which identified and prioritized key players based on their interest and importance. The analysis was conducted by a brainstorming sessions, or by updating existing stakeholder analyses. The second subtask involved systems mapping, where the current status of One Health surveillance was visualized through a workshop or by evaluating and updating existing mappings. Stakeholders collaborated to create a draft map illustrating the system's operation, roles, and relationships, forming the basis for improvement. This process also identified legal and technical barriers/needs for effective data-sharing in a One Health context, which may be addressed during the project's piloting phase. Piloting of One Health surveillance system implementation, designed at the country level, considers the varying development pace of One Health in different countries and addresses locally relevant needs. The approach integrates insights from stakeholder analysis and systems mapping to enhance the effectiveness of surveillance systems in a One Health framework. This deliverable summarizes the activities undertaken during the first year of the project, specifically covering the first two subtasks: stakeholder analysis and systems mapping. It describes a total of 13 stakeholder analysis and systems maps, with a focus of five in the foodborne disease group, four in the zoonotic influenza disease group, and four in the vector-borne disease group. It also outlines upcoming piloting plans that will be conducted over the next one and a half years.