The guideline and the calculation spreadsheet bring you step by step through the development of your mercury inventory on Inventory Level 1. The design of Inventory Level 1 makes it simple to organise and calculate your first national mercury inventory. We acknowledge however that mercury inventory development is generally challenging, especially getting hold of the needed data types for your country. UN Environment, 2019. Toolkit for Identification and Quantification of Mercury Sources, Guideline for Inventory Level 1, Version 2.1, UN Environment Chemicals and Health Branch, Geneva