Eukaryotic genomes are functionally compartmentalized into chromatin domains by their attachment to a supporting structure that has traditionally been termed the nuclear matrix. Present evidence indicates the dynamics of this entity, which requires particular properties of the elements that mediate this kind of interaction. Above all, this is enabled by the so-called 'mass binding phenomenon' by which scaffold/matrix-attachment regions (S/MARs) reversibly associate with ubiquitous factors. Recent investigations and novel techniques have shown that these contacts can be altered by modulators as well as by specific interactions with the components of enhancers and locus control regions.