With half of the world’s habitable land being used for agriculture, monitoring the biodiversity on agricultural land is essential for meeting the objectives of the United Nations Convention on Biological Diversity (CBD). This paper seeks to advance the monitoring of farmland biodiversity in OECD countries by investigating current national initiatives and proposing guidelines for the development of an indicator based on habitat. The proposed approach provides a flexible and pragmatic framework to harmonise reporting from national programmes while accommodating cross-country diversity in contextual factors, including farming systems, climate, biophysical conditions and species pools. To facilitate implementation in the near term, the indicator includes a three-tiered approach to reporting based on data availability, which accommodates countries with limited data resources as well as those that currently have monitoring programmes in place.