The purpose of this primer is to provide students, teachers as well as academic and industry researchers with a succinct account of the chemical and structural features of chromatin and the role that these features play in the maintenance and function of the genetic material. It is universally accepted that DNA is the carrier of the genetic information that is transmitted from parents to their offspring and that it is responsible for the anatomy, physiology and behavior of all individuals throughout development and adult life. Yet, how this information is retrieved and used selectively to allow a fertilized egg to become an organism made up of myriads of different cells and tissues is not as evident and easily understood. Dr Lucchesi, an internationally known researcher and teacher, provides an easily opened window into the role that the complex of proteins and nucleic acids that are associated with the DNA play in mediating gene expression and in responding to environmental circumstances.