This Special Issue celebrates Mendel’s 200th birthday by focusing on exceptions to the Mendelian ‘laws’. Discovery in science is often driven forward more by exceptions than by rules. In genetics, Mendel’s laws of heredity provide the basic ‘rules’. Recent decades have seen an explosion in discoveries that violate these rules, which has driven the field of genetics forward. Indeed, these ‘exceptions’ can shape patterns of inheritance and can have important impacts on evolutionary processes. Genetics Society Executives: Jason B. Wolf, Department of Biology & Biochemistry and The Milner Centre for Evolution, University of Bath, Bath, UK Anne C Ferguson-Smith,, Department of Genetics, University of Cambridge, UK Alexander Lorenz, Institute of Medical Sciences (IMS), University of Aberdeen, Aberdeen, UK