Skills are widely considered as key elements that contribute to the sustainable development of nations and the well-being of individuals. Given the increasing interests in the international comparisons of skills for informing educational policy, it is necessary to understand the definitions, measurement, and development of key skills. Using literature from economics, sociology, and psychology, this article focuses on non-cognitive skills that have a positive effect on life outcomes and can be better developed through education and training. Three non-cognitive skills--grit, self-control and social skills are illustrated and thoroughly reviewed here. Although some progress has been made in developing and measuring non-cognitive skills, there is currently no systematic global measure. Several factors hinder the global monitoring of non-cognitive skills and inhibits effective non-cognitive skills assessment across countries. These include a lack of solid evidence showing which soft skills predict academic and workforce outcomes and how does the strength of this relationship differ by situation.