Natural Climate Solutions – protection, restoration, and improved management of lands and waters that reduce greenhouse gasses – have large climate change mitigation potential. However, lack of comprehensive information on implementation challenges hinders the adoption of Natural Climate Solutions and the delivery of near-term mitigation. Using a global survey of Natural Climate Solutions projects and a systematic review of recent studies, we map 46 constraints in eight categories, yielding 15,572 geo-referenced pathway-constraint observations from 501 studies and projects in 137 countries covering 20 of 22 United Nations subregions. Social-behavioral, Knowledge, and Government-Organizational are the most-reported constraint categories, and lack of policy coordination or implementation capacity the most-observed constraint and most frequently top-ranking constraint for pathways and subregions. Despite broad congruence, top constraint and category rankings vary among subregions and pathways, respectively. We find that projects generally encounter diverse sets of challenges. Without enabling efforts, near-term mitigation from Natural Climate Solutions may remain well below its biophysical potential.