Ribosomal RNA gene repeats (rDNA) are one of the most characteristic regions in eukaryotic chromosomes. The repeats consist of more than 100 tandem units occupying large part of the chromosome in most of organisms. Cells are known to deal with this "unusual domain" in a unique manner. In this review, I will summarize work on rDNA repeat maintenance, focusing mainly on work done by our group, and show that the maintenance mechanism operates by a collaboration of recombination, sister-chromatid cohesion, and chromatin condensation.