The long non-coding RNA Xist directs a remarkable instance of developmentally 
regulated, epigenetic change known as X Chromosome Inactivation (XCI). By 
spreading in cis across the X chromosome from which it is expressed, Xist RNA 
facilitates the creation of a heritably silent, heterochromatic nuclear 
territory that displays a three-dimensional structure distinct from that of the 
active X chromosome. How Xist RNA attaches to and propagates across a chromosome 
and its influence over the three-dimensional (3D) structure of the inactive X 
are aspects of XCI that have remained largely unclear. Here, we discuss studies 
that have made significant contributions towards answering these open questions.