This document discusses impact investing and social performance measurement. It outlines two main approaches to measuring social performance: standardized metrics that allow benchmarking across sectors but lose some relevance and depth, and customized mission-specific metrics that are more actionable for individual organizations but less comparable. Examples are provided of both a standardized GIIRS fund rating and a customized evaluation framework focused on increasing health and well-being outcomes. Grassroots' work assisting portfolio companies through standardized SPI4 and GIIRS assessments and developing customized metrics is also summarized.