A workshop was organised in the Netherlands on 1 September 1999 to improve the National System for Monitoring Greenhouse Gas Emissions. These are the proceedings, including discussion papers, presentations of speakers, reports of discussions and conclusions. It was the task of this workshop to introduce initiatives for adding substance and organisation to the monitoring programme. The starting point of this workshop was the monitoring of policy implementation in the light of uncertainties in emission data. The objectives were elaborated as follows: (1) Per target group: Listing the possibilities for quantitative assessment of the uncertainties of emission estimates. Overall assessment of uncertainties per sector; (2) Per target group: Improving the monitoring of emission reductions; (3) Expertise for follow-up research: Determining the institutions per sector currently equipped to carry out research on uncertainty reduction in emission estimates; (4) Who, what and when? Determining who is going to do what and when to reduce uncertainties in emission estimates; (5) Plan of action: Establishing a general plan per target group to work out the above objectives.