This book summarizes the current knowledge on a cascade of gene regulation levels which operate in the cytoplasm of eukaryotic cells and which has until recently been poorly understood. While transcriptional control of eukaryotic genes has been extensively researched and the understanding of this process has reached very sophisticated levels, post- transcriptional control has received much less attention. As the contributions in this book demonstrate, not only is post-transcriptional control in eukaryotes better understood, it is now thought to be a major player in gene expression control in a number of key processes, i.e. control of cell proliferation, gametogenesis and early development or cellular homeostasis.