The aim of this contribution is to present a general overview about the effect of palladium addition to supported cobalt catalysts. First, the promotion of supported monometallic catalysts by the addition of a second component is described from a general point of view. Then, the properties of bimetallic Pd-Co supported on inorganic oxides are illustrated from the most relevant reports given in the literature. These works have been mainly performed on metallic catalysts under reducible atmospheres for important reactions like hydrogenation of butadiene, Fisher-Tropsch and methane activation under nonoxidative conditions. The last part is concentrated on Pd-Co zeolite-supported catalysts which have exhibited much more resistance to water vapor for lean NO., reduction by CH4 than either Pd or Co monometallic loaded zeolites under net oxidizing conditions. Recent results about the synergism of cobalt and palladium in zeolites and sulfated zirconia are discussed in terms of the effects of catalyst preparation and pretreatment, type of support and gas phase composition on the selectivity and stability of these catalysts for the selective catalytic reduction (SCR) of NO by methane. (C) 2004 Elsevier B.V. All rights reserved.