The rate constants and branching fractions have been measured for the reaction of NO+ with the four butene isomers of C4H8 from 225 to 500 K in a variable temperature-selected ion flow tube. The cis- and trans-2-butene isomers react at the collision rate via charge transfer over the entire temperature range. Isobutene also reacts at the collision rate at all temperatures, primarily through charge transfer; however, an association channel also competes effectively at the lowest temperatures studied because the charge transfer reaction is only 0.02 eV exothermic. The reaction of NO+ with 1-butene is much slower than observed for the other butenes and has a negative temperature dependence. The negative temperature dependence is consistent with the predominant product channel being association. Other products are also observed with 1-butene, including C4H7+ from hydride transfer, C4H8+ from charge transfer at higher temperatures, and several other products involving significant rearrangement and chemical bond formation.