Slow- and controlled-release N fertilizers are designed to increase efficiency and reduce N losses by better synchronizing N availability with plant demand. This paper reviews the use of 15N with these fertilizers to collect quantitative data on the efficiency, residual value and N losses for which relatively few data are available compared with conventional labelled urea and ammonium-based fertilizers. In general, studies of slow-release forms (isobutylidene diurea, oxamide, ureaform) with rice and upland crops show one or more benefits, including improved N uptake efficiency, and reduced N losses via leaching or NH3 volatilization under conditions which favor such losses (coarse textured soils, alkaline pH, respectively). Benefits from residual 15N may accrue in the year following application. Studies with controlled-release 15N-labelled sulfur coated urea (SCU) show benefits in situations such as paddy soils where losses from broadcast urea are a substantial problem. In experiments with 15N polyolefin-coated urea (POCU), rice plant recovery of broadcast conventional urea or ammonium salts ranged from 24 % with losses of 50-45 % with losses of 33 %. Where 15N labelled SCU or POCU was used, the rice recovery ranged from 26 % with losses of 14-72 % with losses of 10 %. Experiments using POCU with corn, barley and potato show similar results. The paucity of published data obtained using 15N points to the need for further studies that will provide concrete evidence for the development of innovative fertilizers with enhanced efficiency and an evidence-based set of recommendations for their selection and use.