Advances in cancer biology have led to the development of screening tests that allow an early diagnosis. Cancer screening is not just the matter of a single individual patient, it is a matter of public health. Screening is commonly viewed as of no harm, when in fact harms are associated with the majority of cancer screening tests. A test should only be used when the potential of benefit clearly outweighs the risks for harm. The data in the literature are not always clear cut and in a lot of cases guidelines are somewhat controversial. What is known and what is unknown about screening tests is quite different from what is believed by the public. The aim of this work is to summarize the different methods and guidelines in cancer screening to help choosing the right test at the right time for the right person.