This document outlines common challenges faced by the UN in developing more impact-oriented monitoring and evaluation systems, and provides potential solutions. It notes that while some UN agencies conduct impact evaluations, many evaluations do not fully address attribution of impacts. It then presents examples of approaches that strengthen causal logic and frameworks to better assess attribution and aggregate evidence of impacts across levels, such as the GEF's Review of Outcome to Impact model and UNDP's meta-reviews of country program evaluations.