Description : More and more open science policies are being developed in countries, universities, research-performing organisations and research-funding organisations around the world. To estimate the advance of open science in different regions, numerous open science monitoring initiatives are emerging, which have the collective characteristic of being heterogeneous, non-comparable and not easily transposable to other geographical areas. These Principles of Open Science Monitoring aim to establish a set of best practices and guidelines that encourage pooling, comparison and reuse of the results of open science monitoring.