DNA double-strand breaks (DSBs) are among the most dangerous types of DNA damage. Unrepaired, DSBs may lead to cell death, and when misrejoined, they can result in potentially carcinogenic chromosome rearrangements. The induction of DSBs and their repair take place in a chromatin microenvironment. Therefore, understanding and describing the dynamics of DSB-containing chromatin is of crucial importance for understanding interactions among DSBs and their repair. Recent developments have made it possible to study ionizing radiation-induced foci of DSB repair proteins in vivo. In this chapter, we describe techniques that can be applied to visualize and analyze the spatio-temporal dynamics of DSB-containing chromatin domains in mammalian cell nuclei. Analogous procedures may also be applied to the analysis of mobility of other intranuclear structures in living cells.