Palladium-mediated cyclization reaction has been recognized as one of the simplest and useful tool for the regio- as well as stereoselective synthesis of carbo- and heterocyclic compounds. In the multi-step synthesis of natural products Palladium-mediated C-H activation reaction is frequently used as one of the most important steps. Further heterocyclic moieties are present in natural products, pharmaceuticals, organic materials, and numerous functional molecules. Therefore, synthetic organic chemists are interested in developing new versatile and efficient syntheses of heterocycles. This book contains brief overview in the construction of heterocyclic rings in various ways under palladium-catalyzed C-H activation.