This paper gives insight into chemical speciation. After a brief introduction, the methods available to study solution state of metal ions and the importance of speciation in biology are discussed through different examples. Speciation of toxic Al-III, beneficial Cu-II and Ca-II and potentially medicinal Pd-II and VOIV in various biofluids and tissues is discussed in order to describe the solution state of these metal ions in an organism. The relevance of ternary complex formation with endogenous biomolecules is emphasised. The importance of the biospeciation of Al-III ion in its transport and involvement in neurological disorders, of the actual chemical form of the insulin-mimetic VOIV complexes in its biological occurrence and Call in mineralization/demineralization processes is discussed. The role of time, i.e., the kinetic aspects of biospeciation, is discussed in the case of the transport of Al-III and Cu-II and some Pd-II, complexes (models of the anticancer Pt-II complexes) in blood serum.