The highly regular and reproducible physical organization of chromosomes in multicellular eukaryotes was first recognized more than a century ago in cytological studies on the lampbrush chromosomes that are found in oocytes arrested at the diplotene phase of meiosis I. At this stage, homologous chromosomes are paired. The two homologs display a similar and reproducible architecture. It consists of a series of loops emanating from the main axis of the chromosome that are arranged in pairs, one from each homolog. In between the loops are regions of more compacted chromatin. We now know that the chromosome architecture of oocyte lampbrush chromosomes is not restricted to these highly specialized chromosomes, but instead is a characteristic feature of chromosomes in multicellular eukaryotes. Like the oocyte lampbrush chromosomes, chromosomes of somatic cells are subdivided into a series of topologically independent looped domains. Underlying this architectural organization are special DNA sequences called boundary elements or insulators. Our research is aimed at understanding how boundary elements subdivide the chromosome into topologically independent domains, and elucidating the genetic and regulatory consequences of this organization.