An overview of the chemistry of the di‐ and trinuclear transition metal polyhydride complexes containing only C5Me5 groups as auxiliary ligands is presented. The synthesis of a series of η5‐C5Me5 polyhydride clusters and their reactivities centered about some typical examples of “multi‐metallic activation” including the cleavage of carbon−hydrogen bonds of alkanes, carbon‐carbon bond of cyclopentadiene, and carbon−carbon double bond of 1,1‐disubstituted alkenes, achieved on the reaction site of the polyhydride‐bridged clusters, are reported. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)