The document summarizes what was learned from assessing research impact as part of the UK Research Excellence Framework (REF) in 2014. Three key lessons learned were: 1) Preparing impact assessments led universities to change practices like implementing impact strategies and tracking impact evidence; 2) The impact assessment process generally worked well but could be improved, such as allowing more nuanced scoring; 3) The REF revealed diverse impacts across all fields and generated insights into how high quality research leads to impacts.