The photochemistry of N+ ions in the daytime thermosphere is studied using the data base of the Atmosphere Explorer C Satellite and it is argued that the reaction O++N(2D) →0+N+ is a major source of N+ ions at altitudes between 250 and 500 km. Close agreement with measurements is obtained by postulating a rate coefficient of 1.3¿10-10 cm3s-1. At altitudes below 300 km, N+ is removed by reactions with O2 but at higher altitudes the reactions of N+ with O and with H are the most important chemical loss mechanisms. We derive empirical rate coefficients of 2.2¿10-12 cm3 s-1 for N++O→N+O+ and of 3.6¿10-12 cm3 s-1 for N++H→N+H+.