Trace metals are accumulated by marine invertebrates to body concentrations higher, in many cases orders of magnitude higher, than the concentrations in an equivalent weight of the surrounding sea-water (Eisler, 1981; Rainbow, 1990; Phillips & Rainbow, 1993). Specific details of trace metal accumulation processes vary within the same invertebrate species between metals, and for the same trace metal between invertebrates, often between closely related species (Rainbow, 1990, 1993). This short review attempts to highlight some of the comparative aspects of the processes involved that are expected and explicable in terms of the chemistry of the respective elements, and those where the physiology of the species involved intervenes to offset predictions from purely chemical principles. Although an appreciation of trace metal chemistry is crucial to an understanding of trace metal accumulation, idiosyncrasies in the biology of the invertebrate (at any taxon level) may intervene to bring about significant and unexpected comparative differences in metal accumulation patterns.