This article reports on recent advances in the area of catalyst regeneration in copper mediated atom transfer radical addition (ATRA) and cyclization (ATRC) reactions using free-radical diazo initiators as reducing agents. The role of reducing agent in both processes is to continuously regenerate the activator (copper(I) complex) from the deactivator (copper(II) complex). As a result, single addition adducts in ATRA and ATRC reactions can be synthesized using very low concentrations of copper catalysts (5-100 pm). Previously, efficient catalysis for both processes required as much as several thousands ppm of copper. It is envisioned that the recent developments in this area could have important industrial implications on the synthesis of small organic molecules, natural products and pharmaceutical drugs.