Genetic epidemiology is a relatively new discipline elucidating and characterising the contribution of genetic factors in disease causation, starting from investigating familial clustering of a disease and ending in identification of the underlying genetic mechanisms. This area of scientific research is a combination of statistical and epidemiological methodology, with molecular genetic technology. Genetic epidemiology contributes to the assessment of cancer risks between family members, by providing the scientific basis for clinical counselling, assisting in therapeutic decisions and cancer prevention. Modelling of cancer in families is informative in describing the modes of inheritance, for both hereditary and environmental causes. Genetic epidemiologists working in the area of cancer hold a unique responsibility in ensuring that results obtained are reliable in guaranteeing the progress of cancer research and in influencing clinical counselling, with potential consequences to the life quality of the patients and their families. This review provides a general introduction into the science of genetic epidemiology, describes the rationale behind the emergence of this field of research and explores the common study designs engaged in the study of genetic epidemiology of cancer.