Oxy-fuel combustion is an emerging combustion technology for capture of carbon dioxide. This technology also creates new conditions for formation of NOx. The present work summarizes the experimental and modelling work performed at Chalmers University of Technology on nitrogen chemistry in oxy-fuel combustion. The major conclusions are that emission of NOx in oxy-fuel combustion strongly depends on the reduction of recycled NO by hydrocarbon radicals (reburning) in the flame zone. Furthermore, the elimination of air-borne nitrogen in oxy-fuel combustion creates an opportunity to reverse the Zeldovich mechanism in order to reduce NOx instead of producing thermal NOx.