DNA repair is typically a multi-step, multi-component process in which proteins detect a DNA lesion; confirm the presence of the lesion; excise the lesion; and replace the excised DNA with freshly-synthesized DNA.  The DNA repair machineries responsible for this task are therefore dynamic systems which must assemble and disassemble at sites of DNA damage.  Understanding the regulation and dynamics of assembly, activity, and disassembly of multicomponent complexes is a challenge which is well-suited to single-molecule experimentation.   We develop novel molecular and instrumental tools for the single-molecule analysis of DNA repair pathways and derive detailed kinetic and strutural insights into the organization and activity of DNA repair complexes.  These include correlative nanomanipulation/fluorescence systems, as well as novel, modular DNA substrates which are particularly well-suited to the study of DNA repair processes.  These tools provide us with mechanistic insight into complex repair processes such as transcription-coupled repair (TCR) and non-homologous end-joining (NHEJ)