Book excerpt: This book addresses the role of tandem repeat polymorphisms (TRPs) in genetic plasticity, evolution, development, biological processes, neural diversity, brain function, dysfunction and disease. There are hundreds of thousands of unique tandem repeats in the human genome and their polymorphic distributions have the potential to greatly influence functional diversity and disease susceptibility. Recent discoveries in this expanding field are critically reviewed and discussed in a range of subsequent chapters, with a focus on the role of TRPs and their various gene products in evolution, development, diverse molecular and cellular processes, brain function and disease.