In this perspective we will discuss recent results on structural aspects of peroxocomplexes of transition metals having the d(0) configuration (V(V), Mo(VI), W(VI)), and show how these may be related to the reactivity of these species in both chemical and biological systems. In addition, we will consider the relevance of structural properties to their involvement as important intermediates in industrial and enzymatic catalysis. These will be related to the behaviour of peroxocomplexes of other diamagnetic transition metals, such as those with d(8) (Pd(II), Pt(II)) configurations.