The Netherlands Ministry of Infrastructure and the Environment, Directorate- General for Water Affairs has asked TNO to identify and work with suitable European partners towards the development of standards for the measurement of underwater sound, with a primary focus on acoustic monitoring in relation to the environmental impact of off-shore wind farms. To date, the licensing requirements for offshore wind farms in the European nations are very diverse. Noise monitoring requirements are generally project specific, with a large influence of the national licensing authorities. The approach adopted in this report is to compare existing monitoring approaches and to identify common ground. The purpose of this report is to propose a minimum requirement for monitoring procedures that fulfils the common requirements. Additional national requirements and scientific needs can lead to extensions of the procedure. These can be defined in cooperation with the national licensing authorities.