This guide aims to: 1) illustrate how investments in ID systems can both positively and negatively impact individuals and their households, through the illustrative stories of Mary, Joy, and Samuel; and 2) provide specific howto guidance to help donors, program managers, and M&E specialists get started in thinking about ID ecosystems. This guide is specifically targeted towards USAID staff and implementing partners who are providing direct support on ID systems, providing advisory services to government ministries, or are trying to find ways to identify beneficiaries in a project or activity (regardless of the sector).