This volume concentrates on those aspects of nuclear structure and trafficking that involve or are relevant to RNA and RNPs. Among the topics presented are fundamental advances and current problems in the structural organization of different subnuclear compartments, Cajal bodies and gems, speckles containing splicing factors, and PML bodies characteristic of ProMyelocytic leukemia. The book also describes recent progress in the dynamic aspects of RNA trafficking and the latest technologies for live cell imaging of mRNA.The key message for readers of this volume is that nuclear structure is much more dynamic than previously believed.