Computer-based simulations have become a critical component of many fields of scientific research and well beyond. The availability of supercomputers permits studies on topics of major societal importance, including climate change, medicine, and energy production, conducted at ever-increasing scales and scope. However, fundamental principles of scientific investigation must be widely enforced to ensure the reliability of and confidence in the results generated. This hinges on our ability to (i) validate (V) them, normally against experimental observations, but sometimes compared to “gold standard” numerical results; (ii) verify (V) them, to ensure that the correct mathematics is used, and (iii) equip the output data with meaningful bounds on errors which come from rigorous uncertainty quantification (UQ).