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 reviewdescribes the stoichiometric reactions of Pd(iv) complexes and discusses their potential mechanism in catalytic reactions (137 references). [ABSTRACT FROM AUTHOR]