In this paper, fundamental issues of the NSR technology are addressed. The reaction paths and the mechanism involved in the storage of NO (x) and the relevance of the proximity between the noble metal and the alkali or alkaline-earth component of the catalyst are discussed first. Then the release of NO (x) , the reaction pathways of NO (x) reduction by different reducing agents, and the mechanisms involved in the formation of N-2, NH3 and N2O are illustrated. The use of the combined technologies LNT + SCR and DPNR is addressed next and key aspects that highlight the synergies of the individual technologies are discussed. Finally, the perspectives of the NSR technology are outlined.