Although the chemistry of Pd(0), Pd(I) and Pd(II) is well established, high oxidation state Pd(IV) complexes are less well-known. This situation has highly changed in recent years. Many well-defined Pd(IV) complexes has been isolated and characterized, providing evidence for a series of proposed Pd(II)/Pd(IV) catalytic reactions. A deep understanding of the behavior of Pd(IV) complexes could lead to the design and development of novel reactions that could not be accessed by traditional Pd(0)/Pd(II) chemistry. This critical review describes the stoichiometric reactions of Pd(IV) complexes and discusses their potential mechanism in catalytic reactions (137 references).