The relationships among in vivo chromatin structures, chromosome organization and genome function must be understood in order to reveal the hidden regulatory information in our genomes. Rather than being stable architectural features, it appears that chromatin and chromosome conformations at all levels are highly dynamic, which is the key to their function. Studies in recent years have elucidated long-range interactions or folded chromatin conformations that play significant roles in gene regulation. Most recently, intrachromosomal associations and co-associations with shared nuclear transcription compartments have been discovered in mammals, with the potential to greatly expand our view of how the genome is regulated.