Advances in Genetics continues to present articles that are of interest to both human and molecular geneticists. Volume 37 offers a single chapter, written by I.F. Zhimulev, in which Dr. Zhimulev undertakes thelaborious task of presenting an in-depth and detailed account of the various aspects of heterochromatin organization in the mitotic and interphase polytene chromosomes. It also includes details concerning the organization of heterochromatin at high resolution are also analyzed.