This paper provides a summary of the assessment report of the WorldMeteorological Organization (WMO) Expert Team on Weather Modificationthat discusses recent progress on precipitation enhancement research.The progress has been underpinned by advances in our understanding ofcloud processes and interactions between clouds and their environmentwhich, in turn, have been enabled by substantial developments intechnical capabilities to both observe and simulate clouds from themicrophysical to the mesoscale.We focus on the two cloud types most seeded in the past: winterorographic cloud systems and convective cloud systems. A key issue forcloud seeding is the extension from cloud-scale research to watercatchment-scale impacts on precipitation on the ground. Consequently,the requirements for the design, implementation and evaluation of acatchment-scale precipitation enhancement campaign are discussed.The paper concludes by indicating the most important gaps in ourknowledge. Some recommendations regarding the most urgent researchtopics are given to stimulate further research.