The results of experimental and theoretical studies of chemical reactions in nonequilibrium plasmas are reviewed. Special attention is given to processes stimulated by vibrational excitation of the ground electronic state of the reacting molecules in the plasma. General patterns in the kinetics of these reactions are discussed, and the optimum discharge parameters for maximum energy efficiency are noted. Specific plasma-chemical processes--the dissociation of CO$_2$ and H$_2$O and the synthesis of nitrogen oxides--are described. Experimental results are presented for hf, microwave, glow, plasma-beam, and non-self-sustained discharges, for plasma radiolysis, etc.