This document summarizes lessons learned from a capacity development program to support climate change mitigation and transparency efforts in 38 countries. Key lessons include: (1) assigning climate relevance to financial flows and obtaining private sector data is challenging; (2) data availability and quality for transparency remains a fundamental issue; and (3) country-driven approaches that build on existing systems through engagement over time are most effective. The program delivered various outputs to support NDCs and transparency, but further targeted technical support is now needed for implementation.