This thesis presents the results of the analysis of the reaction: π(^+)d →d π (^+) π (^+) π (^-) at 11.7 GeV/c incident momentum. The experiment from which the data were obtained is described and the method of selecting the sample of 1675 events belonging to the channel is discussed. The reaction is found to be dominated by p production with some f production. There is also a d(^π++) non-resonant peak in the dπ(^+) mass spectrum. The three pion effective mass spectrum is dominated by threshold enhancements of the p π(^+) system, the A(_1), and the f π(^+) system, the A(_3). A spin parity analysis indicates that the A(_1) has J(_P) = 1(^+) while the A(_3) has J(^P) = 2_^-). Neither of these enhancements are found to conserve s-channel helicity, but t-channel helicity is found to be compatible with the results on A(_3) production and almost compatible with those on A(_1) production. A Longitudinal Phase Space analysis of the channel is described and the results of a kinematical model to explain A(_1), and A(_3) production are presented and critically discussed. The results of a search for coherent A(_2) production are described and a small enhancement which may be identified with the n(_N) (1080) meson is studied.