The link between grain refinement and casting defects such as hot tearing, cold cracking and macrosegregation is recognised for decades. Actually, the grain refining practice serves primarily this purpose – to produce high quality defect-less billets/ingots. The mechanisms behind this connection are, however, rather complex and multi-dimensional. Without recognising these mechanisms and their complexity and interrelation, the occurrence of defects under particular conditions remains a mystery that is almost impossible to decipher. Different mechanisms may act in different proportions and drive the system in different directions, depending on the particular casting conditions. So oversimplification of the analysis leads necessarily to the complexity. On the other hand, knowing these complex mechanisms makes the analysis of the casting defects and the ways for their prevention a rather transparent and simple task. In this presentation, the interrelation between the grain refinement and the casting defects will be explained and illustrated with the data published in TMS Light Metals proceedings over the last 50 years.