The mechanism by which ribosomal RNA is synthesized has been a topic of intensive research for nearly 30 years. However, in 1981 the first in vitro transcription system for ribosomal RNA from a eukaryote, mouse ascites cells, was reported, followed rapidly by similar systems in a variety of other eukaryotes, which were revealed by a relatively small number of research groups. This monograph is the first to bring together the results and opinions of all these groups.