This document discusses measuring the impact and return on investment for corporate social investment programs. It notes that there is increasing pressure from funders to demonstrate the effectiveness of programs. Impact can be measured prospectively, ongoing, and retrospectively to inform investment decisions. Key applications include determining whether projected costs and benefits indicate a favorable investment, aiding course correction during implementation, and informing future decisions by looking back at costs and outcomes. Impact should be measured across economic, social, and environmental dimensions over time. Challenges include determining the appropriate indicators and evaluating intangible impacts, but overall impact measurement can provide accountability and help improve development effectiveness.