Lucas et al. report the visualization of V(D)J recombination of the immunoglobulin heavy-chain gene (Igh) in living pro-B cells. Despite the huge distances separating V coding sequences from D-J sequences (~2 Mb), the authors document an astonishingly rapid rate of remote associations. The key to speed is contraction of the Igh chromosomal domain. These findings provide a foundation for understanding long-range regulatory interactions in a variety of developmental processes, including the patterning of vertebrate limbs.