This Timeline article looks back at 40 years of research into the inherited genetic basis of cancer and the insights these studies have yielded. Early epidemiological research provided evidence for the 'two-hit' model of cancer predisposition. During the 1980s and 1990s linkage and positional cloning analyses led to the identification of high-penetrance cancer susceptibility genes. The past decade has seen a shift from models of predisposition based on single-gene causative mutations to multigenic models. These models suggest that a high proportion of cancers may arise in a genetically susceptible minority as a consequence of the combined effects of common low-penetrance alleles and rare disease-causing variants that confer moderate cancer risks.