Measurements of atmospheric parameters made by the Atmosphere Explorer-C satellite are used to identify mechanisms for the production and loss of N+ ions in the ionosphere. The main source below 250 km is found to be photodissociative ionization of N2. Above 250 km the reaction O+(4S)+N(2D) →k1 N+(3P)+O(3P) is dominant; k1 is found to be 5 +7-2¿10-11 cm3 s-1. A possible minor source of N+ is the reaction O+(2P)+N2→k2 N+NO where k2=1+-1.5¿10-10 cm3 s-1. Photoionization of N(4S) and dissociative charge exchange of He+ with N2 constitute detectable sources above 350 km. Charge exchange of N+ with O is identified as a significant sink above 300 km. The rate coefficient for this reaction is 5+7-2¿10-13 cm3 s-1.