Conjugated dienes and polyenes are typically synthesized by sequential introduction of C=C bonds. Here, we report a practical and scalable, catalytic dienylation that is highly regio- and stereoselective for both C=C bonds. The reaction is enabled by a stereoselective palladium-catalyzed cross-coupling that is preceded by a regioselective base-induced ring opening of readily available sulfolenes. The dienylation reaction is particularly useful for the synthesis of synthetically challenging dienes containing cis double bonds. We also show that the reaction can serve as a synthetic platform for the construction of conjugated polyenes.