Although definitive information on the structure and function of chromatin has not yet been obtained, current work leads us to predict that in the very near future the properties of chromatin and their molecular basis will be understood. It is our hope that this special issue, which details recent advances in the studies of chromatin structure, conformation of intracellular DNA, and gene expression, will be helpful to those now pursuing that goal and will stimulate others to participate in this challenging and promissing endeavor.In this special issue, the following articles are included.(1) Iwai, K. (Institute of Endocrinology, Gumma University).The past and future of chromatin research.(2) Fukada M. (Department of Microbiology, Aichi Medical University).Higher order structure of biological by active DNA in Fukaryotes.(3) Muramatsu, M. (Department of Biochemistry, Cancer Institute, Japanese Foundation for Cancer Research).Organization of Eukaryotic Genes and Splicing.(4) Oba, Y. (Faculty of Pharmaceutical Sciences Kanazawa University).Structure and function of active chromatin.(5) Nakamura, H., Kano, Y., Ishii, S., Miyashita, T., Nagata, A., and F. Imamoto, (Research Institute for Microbial Diseases, Osaka University).Structure and function of prokaryotic nucleoids.(6) Oda, T. (Department of Biochemistry, Cancer Institute, Okayama University Medical School).Structure and function of SV40 chromatin.