Fluid reasoning is the ability to figure out abstract, novel problems not reliant on specific knowledge. Individual differences on this ability predict school success, longevity and morbidity, socio-economic outcomes and mental and physical health. However, ‘gold standard’ tests such as the Ravens Matrices and Cattell Culture Fair test are expensive, preventing access by less well-resourced countries, practitioners, and labs, and have a limited number of items, preventing use in longitudinal or ‘experience sampling’ studies. The Open Matrices project will (1) develop, (2) validate and (3) make available an effectively unlimited set of fluid reasoning items to the global community.