Leiden University is the oldest university in the Netherlands. Since its foundation in 1575, Leiden University has maintained an impressive international profile. The current student enrolment is around 15000 students. Leiden University still has an international outlook and orientation and maintains numerous contacts with academic institutions all over the world. Leiden University consists of nine faculties having more than 100 departments. Leiden University has a firmly established position among the top research institutes of Europe in many fields, including the natural sciences, medicine, social and behavioural sciences, law and the arts. The Department of Toxicogenetics (formerly the Department of Radiation Genetics and Chemical Mutagenesis) is part of Medical faculty, having three groups (DNA repair and genomic instability, Mutagenesis and genomics). This department comprises fundamental and applied research focusing on the interactions of chemical agents or radiation with nucleic acids, the biological consequences of such interactions and genetic/cancer risk assessment, and biological dosimetry. To make rational judgment for the protection of people against the adverse effects of genotoxic agents, it is necessary to extrapolate to low doses. The objectives are focused on generating a detailed knowledge of the mechanisms by which genotoxic agents such as ionizing radiation induce genetic alterations and cancer. This can be achieved by developing and applying different assays, to identify DNA lesions, their frequency or induction and their repair kinetics, to analyse the genetic alterations to DNA damage exposure (chromosomal alterations) and to estimate the genetic and cancer risks.