This document summarizes information from a STEM Funders Network initiative on building STEM learning ecosystems. It provides background on the goals of developing strong cross-sector collaborations and partnerships to improve STEM education. It outlines the key elements of STEM learning ecosystems, including partnerships across various sectors like K-12, out-of-school programs, higher education, and businesses. It also describes the technical assistance and support provided to communities participating in the initiative's cohorts, including the development of communities of practice to facilitate peer learning.