Over the last few years remarkable progress has been accomplished with respect to our understanding of nuclear structure and trafficking. This volume concentrates on aspects that involve or are of relevance to RNA and RNPs. Topics include fundamental advances and current problems in the structural organization of different subnuclear compartments: chromatin, nucleolus and perinucleolar compartment, Cajal bodies and gems, speckles containing splicing factors, as well as the PML bodies characteristic of ProMyelocytic Leukemia. It also describes recent progress in the dynamic aspects of RNA trafficking and in the latest technologies for live cell imaging of mRNA. The major general message of this volume is that nuclear structure is much more dynamic than previously anticipated.