This document provides a proposal for the establishment of a GCOS Surface Reference Network (GSRN). Reference quality observations are directly traceable to the International System of Units (SI) standards and include full documentation of all components of their uncertainty. Such observations respond to the need for monitoring the changes that occur in the climate and ensure greater confidence in the assessment of future climate change and variability. Such a network will also support timely political decisions around mitigation and adaptation. A GSRN will contribute to the improvement of the current climate observing system. However, benefits would accrue much more immediately, through improved observational understanding and better methods of observation leading to improvements in numerical weather prediction and disaster and emergency response systems. The principal benefits of a reference network are: well characterised time series that can be used with confidence at network sites; improved instrument performance that transfers down to other broader global regional and national networks; support and characterisation of wider networks; robust calibration/validation of satellite data; improved process understanding and model validation.