Science & Technology Trends: 2020-2040 provides an assessment of emerging or disruptive Science & Technologies (S&T) and their potential impact on NATO military operations, defence capabilities, and political decision space. This assessment draws upon the collective insights of the NATO Science & Technology Organization (STO), its collaborative network of over 6000 active scientists, analysts, researchers, and engineers, and associated research facilities. These insights have been combined with an extensive review of the open-source S&T futures literature and selected national research programs.