This report provides IPCC guidelines to countries on how to estimate and report to the UNFCCC their HFC-23 emissions from HCFC-22 manufacturing in their greenhouse gas inventories. It outlines options and issues for good practice guidance in the national inventory management for HFC-23 emissions, including methodological issues, reporting and documentation and inventory quality. Measurement of HFC-23 emissions using a Tier 2 approach is highly accurate because data reflect conditions specific to each plant. Where measurements are impossible, Tier 1 default emissions data must substitute for plant-specific data. The report recommends daily sampling at either the process vent or within the process itself for very high-quality estimate.