UNSTRUCTURED Background: The term Community Health Worker (CHW) can apply to a wide range of individuals providing health services and support for diverse populations. Very little is known about the role of CHWs in Europe who work in non-clinical settings and who promote sexual health and prevent HIV/STI among gay, bisexual and other men who have sex with men (MSM). Objective: This paper describes the development and piloting of the first European Community Health Worker Online Survey (ECHOES) as part of the broader European Union (EU) funded ESTICOM project. The questionnaire aimed to assess the knowledge, attitudes, and practices of CHWs providing sexual health services to gay men, bisexual men and other MSM in European settings. Methods and analysis: ECHOES comprises of three superordinate domains divided into 10 subsections with 175 items (routed) based on a scoping exercise and literature review, online pre-piloting and a Europe-wide consultation. Additional piloting and cognitive debriefing interviews with stakeholders were conducted to identify comprehension issues and improve the clarity, intelligibility, accessibility, and acceptability of the survey. Psychometric properties including internal consistency of the standardised scales used as part of the survey including internal consistency were examined. The final survey was available in 16 languages. Results: Recruitment closed on 31 January 2018. A total of 1,035 community health workers were available for analysis, after application of exclusion criteria. Discussion: The findings of the survey will be available in late 2019 and will help characterise for the first time, the diverse role of CHWs who provide sexual health services to gay men, bisexual men and other MSM in Europe. Importantly, the data will be used to inform the content and design of a dedicated training programme for CHWs as part of the larger European Union (EU) funded ESTICOM project and provide recommendations for EU strategies to improve sexual health in general and to reduce HIV, viral hepatitis and other STIs incidence and prevalence in particular.