IQ is a psychological indicator with exceptional psychometric properties and substantial real-life predictive power. Behavior genetic results have long suggested that IQ is strongly heritable, that is, inter-individual IQ differences are mostly due to genetic differences, and that the effects of the environment shared by siblings, such as the family's place of residence or socioeconomic status, is minimal. Recently these observations were confirmed by quantitative genetic studies of unprecedented sample sizes, SNP heritability studies combining quantitative and molecular genetic approaches, and genome-wide association studies identifying specific genetic variants underlying IQ. Genome-wide association studies enable the creation of polygenic scores which correlate with actual cognitive ability at approximately r=0.3. The increasing understanding of the genetic basis of IQ, especially the use of polygenic scores validates previous quantitative genetic paradigms and clears the path for several applications in psychology, but it may also be the source of bioethical dilemmas.